Amphibious Employment of the 4.2-inch Mortar
Compiled & edited by Jack Butler, veteran of the 82nd Chemical Mortar Battalion
This history of World War II mortar gunboats is compiled from portions of the following two volumes of the 3-volume history of the Chemical Warfare Service (CWS) published by the Army's Office of Military History, plus reflections of the compiler/editor on amphibious training in Empress Augusta Bay, Bougainville, Solomon Islands:
Volume II, From Laboratory to Field, Chapter VI, "Chemical Mortars and Shells"
Volume III, Chemicals in Combat, Chapter XIII, "The Chemical Mortar in the Pacific"
1942 - Developing doctrine and experimenting
July 1943 - Sicily
Spring 1944 - Saipan, Marianas Group - aborted operation
21 June 1944 - Bougainville, first successful amphibious combat operation
August 1944 - Training in Empress Augusta Bay, Bougainville, Solomon Islands
15 September 1944 - Peleliu, Palau Islands: first LCI(M) combat use
20 October 1944 - Leyte, Philippine Islands
9 January 1945 - Luzon, Philippine Islands
19 February 1945 - Iwo Jima, Bonin Islands, northwest Pacific basin
1 April 1945 - Okinawa, the Ryukyus Islands, northwest Pacific basin
1942 - Developing doctrine and experimentingBefore the War Department authorized the high explosive mission for the 4.2-inch mortar and before any chemical mortar units reached the theaters of operation, the CWS was developing doctrine for the use of the mortar in assault landings. Beginning in the summer of 1942, this doctrine was developed at the Amphibious Training Center, Camp Edwards (Buzzards Bay), Massachusetts, and continued at Camp Carabelle, Florida (later Camp Gordon Johnson). [Vol. III, p. 520]
The CWS experimented with mortars mounted on landing craft, including the LCIs (Landing Craft Infantry) and LCTs (Landing Craft Tank). It took the view that mortars could support an amphibious assault in the crucial period of an invasion, after the naval and air bombardment let up so that troops could land. Mortars could not be placed directly on the bottom of landing craft since there was no way to keep the recoil from kicking mortars backward when the piece was fired. In addition, the terrific pounding might damage the bottom of the vessel. Technicians rigged an oblong wooden frame, filled with a mixture of sand and sawdust, on the floor of the craft. A thick slab of wood (several sheets of plywood) grooved to take the bottom Y-spade of the baseplate, sat on top of the sand-sawdust filling. The Amphibious Training Command, Camp Carabelle, Florida, to which CWS sent the firing platform, saw the utility of the device and asked the service to design a standard model. [Vol. II, pp. 136-7]
July 1943 - SicilyElements of the 3rd Chemical Mortar Battalion sailed from North Africa for Sicily prepared to support the 3rd Division with mortars mounted on six assault craft, a measure made unnecessary with the attainment of tactical surprise.
Despite these preparations in the European theater, the amphibious employment of the 4.2-inch mortar occurred only in the Pacific. Colonel Unmacht first suggested the technique to Navy officers in July 1943 at the Makua, Oahu demonstrations. The Navy liked the idea and played around with it for almost a year. The advantage of the mortar boat plan was that it provided assault troops with heavy effective fire during that period in the landings when they were most vulnerable the time between the lifting of the naval bombardment and the establishment of supporting weapons on shore.
In a remarkable case of CWS-Navy cooperation, the kind which typified the activities of Colonel Unmacht on Oahu, there emerged a new type of craft, one armed with 4.2-inch mortars. It was not born without difficulty. The Navy provided three LCTs (Landing Craft Tank) for the project and later several LCIs (Landing Craft Infantry). The latter, dubbed LCI(M), were to become the standard mortar-landing craft.
Spring 1944 - Saipan, Marianas Group - aborted operationThe first attempt to get the mortar boats into action proved abortive. Favorably impressed with the vessels during seven tests again run at Makua, the Navy decided to use three of the 4.2-inch-mortar-equipped LCTs in the invasion of Saipan. These plans went awry during the assault rehearsal off Kahoolawe, one of the Hawaiian group. Each of the three LCTs was lashed to the deck of a landing ship tank (LST), for the decision had been made for the smaller vessel(s) to make the long journey to the scene of operations in this piggyback fashion. During an extremely heavy sea two of the LCTs broke their lashing and were washed overboard. The third LCT escaped this fate only to be destroyed at Pearl Harbor when its LST suddenly exploded. Fifty-nine people lost their lives in the resulting holocaust. [Vol. III, p. 521]
21 June 1944 - Bougainville, first successful amphibious combat operationOn this date, Company B, 82nd Chemical Mortar Battalion, under command of Captain Joseph Van Yush, employed 4 LCVPs (Higgins Boats) in support of the Fijian Infantry Regiment. The boats, with one 4.2-inch mortar in each and manned by a section from 2nd platoon, Company B, laid a smoke screen to cover the Fijian landing at the mouth of the Jaba No.1 River behind Japanese lines.
August 1944 - Training in Empress Augusta Bay, Bougainville, Solomon IslandsFollowing the 21 June successful employment of 4.2s from Higgins Boats and the close of the Second Battle of Bougainville in March 1944, the outpost line of the beachhead in front of the 37th and Americal Divisions had been extended. Preparations were made for General Griswold's XIV Corps and its 82nd Chemical Mortar Battalion to join General Kruger's Sixth Army in the recapture of Luzon, the main island in the Philippines. Accordingly, the "4-Deucers" spent several weeks on the water of Empress Augusta in a variety of landing craft. The first, and perhaps one not given adequate attention in later studies, was the Landing Craft Vehicle/Personnel (LCVP). Capable of landing 36 troops and their equipment or 12 men and a Jeep, the LCVP was ideal for use with one 4.2-inch mortar and the mortar squad. The LCVP is the Higgins boat of WWII fame and, in the words of General Eisenhower, "Andrew Higgins is the man who won the war for us." See the website of The Higgins Boat Project and click on "The LCVP Design" item.
Mortar boat combat operations discussed in the references focus on the critical task of supporting assault forces in initially gaining and holding a beachhead, correctly emphasizing the use of LCI(M)s. But situations like that on Bougainville presented many opportunities where a platoon of 4.2-inch mortars, operating from four LCVPs with one squad in each, could render very effective support after the beachhead had been established. On Bougainville in March 1944 the beachhead was secure and its only reason for existence was to secure three airfields, primarily for strikes against the Japanese bastion of Rabaul in New Britain to the north. It took the Japanese from December 1943 to March 1944 to realize we didn't want the whole island. Guess they weren't carin' for sharin'.
With the 4-boat LCVP mortar fleet, we could range up and down the beach on either side of the perimeter. Training exercises involved firing HE and WP into areas up to 4,500 yards from the beach. Very often we fired from 600 yards to the beach and into the jungle bordering it where trails were most likely to exist and where we could best observe our impacts. Although we had no assigned targets, it became apparent that patrol actions or a reconnaissance in force within 4,000 yards of the beach might benefit from such readily available support at distances from the perimeter that could not be attained from land. Such was the successful combat employment of 21 June, reported above.
Controlling the four LCVP mortar boats from the "flagship" (the boat the platoon leader chose to ride in) was generally effective by use of the "walkie-talkie" radios, which were strictly line-of-sight and not too bad over water at distances of 1,000 yards. As a backup, we learned semaphore and communicated between boats with the wigwag of flags.
Other craft we trained on included the Landing Craft Mechanized (LCM) small, about 45' in length with a ramp for loading/unloading wheeled or tracked vehicles. Our local Seabees operated a sawmill and were able to produce the firing platforms described in previous sections. There was no shortage of lumber, especially after XIV Corps Engineers cleared several acres for a huge ration dump. The major difficulty was breaking saw blades on all the shrapnel embedded in the tree trunks. Mounting four mortars, two in the well deck and one on each side of the wheel on the upper rear deck, worked well as long as we fired salvoes. Firing a volley of four guns while running toward the beach was like putting on the brakes.
Despite our interesting training, the Navy probably had previous plans for the invasion of Luzon. The 82nd Chemical Mortar Battalion landed on D-Day, 9 January 1945, with the 40th Division. It was not called on to man the LCI(M)s. That honor would go to the 98th Chemical Mortar Battalion supporting both XIV Corps and I Corps landings in Lingayen Gulf.
15 September 1944 - Peleliu, Palau Islands: first LCI(M) combat useBefore the end of the Marianas campaign, the Navy revived the mortar boat project. This time the weapons were to be on LCIs, four of which were to be fitted out, each with three 4.2-inch mortars. One weapon was mounted forward in the center of the boat, the others amidships, one on the port side and one on the starboard. All fired forward, over the bow. Beneath the mortar mounts the deck was reinforced with steel plating. The two forward troop compartments served as magazines for mortar ammunition, a normal complement being 1,200 rounds. Major Leland E. Anderson of the 88th Chemical Mortar Battalion commanded the mortarmen who had come from diverse sources: 4 officers from the 88th, 12 enlisted men from the 91st Chemical Mortar Company, and 4 officers and 88 enlisted men from the 111th Infantry Regiment. Designated as LCI(M) numbers 739, 740, 741, and 742, the mortar boats were earmarked for the campaign in the Palaus. The four boat crews prepared for the operation by test runs at the Makua site in the Hawaiian Islands and by participation in the invasion rehearsal at Guadalcanal.
Led by Major Anderson, the four LCI(M)s made history as they were the first LCI(M)s to fire 4.2-inch mortars from the sea against an enemy. On 15 September 1944 they supported the III Amphibious Corps landings by the 1st Marine Division on the island of Peleliu. During the initial run on the island, moving at a speed of less than three knots, they fired 100 rounds of HE from positions 3,000 to 1,300 yards offshore at the very slow rate of one round per mortar every two minutes. As the mortar boats drew closer, the range of the weapons was decreased by reducing the number of increments. This method of fire was sometimes known as Plan Baker. Mortar fire covered the northern flank of White Beach for a depth of 200 to 300 yards, with only a few water bursts being observed. These supporting boats lifted their fire as friendly aircraft strafed the beach, only to resume it from fixed positions 900 to 1300 yards offshore. The mortars then placed harassing fire upon the dense woods, areas of defilade, and possible enemy observation posts and installations on the hill to the northwest. Good dispersion resulted from this fire, delivered at ranges varying between 2,100 and 2,610 yards, although the thick foliage and defiladed areas precluded effective observation. The employment of mortar boats from fixed offshore positions was often designated Plan Charlie.
A second mission at Peleliu began about an hour after the end of the first and consisted of the bombardment of the same hill area northwest of the beach area, its rocky top now a mass of rubble. Firing at ranges of 3,200 yards, each mortar delivered two rounds of high explosive shell a minute from more or less stationary positions 1,800 to 2,100 yards offshore. While winds and currents at Peleliu were not strong enough to cause excessive drift, the little movement that did occur made precise firing difficult. Radar ranges taken by LCI(M) 741, the flagship, as well as visual cross-bearings and fall of shot observations, helped to fix the ship positions and to determine ranges as the vessels drifted or maneuvered. In any event, the resulting dispersion was not detrimental to the general mission of laying down area harassing fire. Enemy mortar fire during the two runs proved ineffective, most rounds falling short.
Firing from a moving boat had little effect upon the accuracy of the mortar. In rough seas lateral, but not vertical, accuracy was impaired. And the latter was the more important factor because of the possibility of hitting friendly troops as they advanced inland.
Two days later, on 17 September, the same four mortar boats supported the 81st Division assault on the island of Angaur, also in the Palaus. Instead of executing Plan Baker immediately, as had been done at Peleliu, all craft fired an abbreviated Plan Charlie: 6 to 10 rounds per mortar per minute for 7 minutes from positions 2,400 yards offshore. The group of gunboats then moved toward shore at a speed of four knots. It took 10 minutes to come within 1,000 yards of the beach, during which time each of the mortars fired at the rapid rate of 20 rounds per minute. Excessive noise made the commands of the fire control officer virtually inaudible while smoke did much to hinder observation. Despite these handicaps most of the 2,345 rounds landed in the target area and inflicted extensive damage.
On the following day, our infantry on shore, pinned down by rifle and machine gun fire, called for supporting fire from our mortars. There was time for only 2 runs, one of 6 and the other 8 minutes, at speeds of 4 and 3 knots, respectively. The target area, located on the northwest end of the island, varied in width from 500 to 850 yards and extended from the shore to a depth of 900 yards. At an average firing rate of 5 rounds per mortar per minute, 830 rounds fell in the area. Mine fields prevented the mortar boats from approaching closer than 1,500 yards from shore, but the effectiveness of the mortar barrage was such that 3 minutes after it had been lifted the troops, previously pinned down by enemy fire, encountered no opposition on advancing into the heavy woods.
At the end of the Palau operation CWS officers recommended that mortars on boats making the run toward the shore maintain a constant elevation of 1,000 mils (56.25 degrees above horizontal) with traverse dependent upon the course of the craft. They also suggested that mortar fire be kept within 400 yards of the assault troops and that mortar boats maintain an offshore range of between 3,200 and 2,000 yards as a precaution against enemy fire. The latter recommendation was disregarded, and subsequently mortar boats came within 500 yards of the shore. Suggestions about the more effective installation of the mortars on the boats were either not adopted or proved to be without merit. [Vol. III, pp. 521-25]
20 October 1944 - Leyte, Philippine IslandsTwo groups of mortar boats supported the landings at Leyte Gulf on 20 October 1944. Each group was composed of four LCI(M)s, with two LCI(A)s serving as ammunition boats. Major Richmond H. Skinner, CWS, exercised overall command of mortar firing personnel of the groups. Men from the 98th Infantry Division stationed at Hawaii manned all twenty-four mortars in the two groups and fired in support of the 7th and 96th Divisions under XXIV Corps.
One of the boat groups executed Plan Baker. It moved in at the slow speed of 1« knots, firing from 2,200 to 400 yards offshore and expended about 480 rounds of HE in 20 minutes on Orange Beach 2. A slow rate of fire of two rounds per gun per minute was maintained while the range was gradually reduced. Twelve hundred yards from shore, enemy mortars or howitzers straddled the mortar boats without causing casualties or damage. The weather was ideal and the sea relatively calm.
That group then fired from fixed positions (Plan Charlie) on enemy positions in the ravines and on reverse slopes of the Labiranan Head Ravine and Catmon Hill area, silencing the Japanese guns that had been plaguing the troops on the beaches. According to one Navy observer, this mission, completed without observation from computed data and fired at distances from 1,000 to 1,900 yards offshore, proved accurate beyond expectations.
The second group, meanwhile, was firing on Yellow Beach targets near the town of Dulag. Spaced from 50 to 75 yards apart, these mortar boats began firing 1,500 yards from shore and continued as they slowly moved into positions 400 yards from the beaches. This bombardment blanketed an area 800 yards wide and 900 yards deep. Fifteen minutes after this beach-shelling phase, the mortars began firing on call. Within the next five hours, infantry requests for support resulted in the expenditure of almost 4,500 rounds. During this "on-call" phase, the boats slowly drifted to the left, directing fire on enemy targets on the south bank of the Daguitan River and on the approaches of a bridge across that river, an effort that drove enemy tanks from the road leading to the bridge.
After the first mortar boat group completed its missions on Orange Beach 2, it returned for resupply to the transport area twelve miles to the rear. It had no further missions that day. Thereafter, until they withdrew on the morning of A plus 5, the mortar boats of this group used smoke pots to screen the large vessels from air raids during the hours of both morning and evening twilight.
Both mortar boat groups received written commendations from the leaders of the flotillas they supported, as well as from the commanders of Amphibious Groups 3 and 6. Admiral Forrest B. Royal, commander of Group 6, stated: "The performance of LCIs equipped with 4.2" Army mortars was excellent. The mortar fire was delivered in a rapid, accurate, and effective manner." Admiral Royal compared the effectiveness of the mortar boats and the rocket boats. While praising the "highly successful accomplishments" of both weapons, he pointed out that the rocket boats were of no further use after their single crash concentration because they were unable to reload in time to continue covering the assault waves. On the other hand, the mortars could fire without letup. [Vol. III, pp. 525-6]
9 January 1945 - Luzon, Philippine IslandsThree separate mortar boat groups supported the Sixth Army landings in Lingayen Gulf on Luzon. The two boat groups that had served in the previous Leyte operations in October 1944 proceeded to New Guinea to pick up men from the 98th Chemical Mortar Battalion. This step was made necessary when four LCIs, which had served as ammunition carriers, LCI(A)s, during the Leyte action, were converted to mortar boats, LCI(M)s. All mortar craft participated in the mid-December training exercises in Huon Gulf, New Guinea, which simulated the landings that were to take place at Lingayen Gulf, Luzon.
One of the three mortar boat groups, Task Unit 79.8.1, was composed of six LCI(M)s and commanded by Lt. Comdr. G.W. Hannett, USN, and accompanied by Maj. Richmond Skinner, 88th Chemical Mortar Battalion. A second group was formed from the converted ammunition carriers, with mortarmen from the 98th Chemical Mortar Battalion. The third group had its mortars manned by Marines, trained by and under the supervision of a detachment from the 98th Chemical Mortar Battalion.
The six mortar boats of Task Unit 79.8.1 supported the XIV Corps landings on the beaches of Lingayen Gulf and then stood ready to furnish fire on call for the 185th Infantry, 40th Division, in its movement inland. The mortar boats were to be ready for any special mission that might arise, as well as to smoke the transport area during the hours of morning and evening twilight.
General control of the mortar boats was in the hands of the task group and task unit commanders, but individual vessels maintained the responsibility for engaging specific targets. Training of the mortar crews continued even while en route to the objective. Navy men received instruction in the handling of the mortar in the event casualties would bring the need for extra hands.
On 9 January 1945, climatic conditions were favorable, with a mild offshore wind and visibility ranging from fifteen to twenty miles. The swell of the sea caused some landing difficulty but did not seriously affect the mortar missions. Shortly after 0600 the six mortar boats of Task Unit 79.8.1 broke off from the main body, maneuvering in zigzag fashion through the armada of support ships to their initial positions 2,500 yards from shore. A few minutes later, an enemy suicide bomber (Kamikaze) swooped down in attack. The Japanese plane itself inflicted no damage, but five men from an LCI(M) received wounds from a 20-mm shell fired at the enemy by another vessel in the formation. At 0845 the six mortar boats moved into their attack positions, and fifteen minutes later they began their scheduled fire.
The LCI(M)s moved forward, blanketing the beaches to a depth of almost 350 yards with accurate and devastating fire. As the craft approached the shore the number of propellant charges on the mortar shells was progressively decreased. Precise ranges were determined by radar on several of the LCI(M)s and passed to the others by prearranged visual signals. The only return fire came from enemy mortars whose shells fell 600 yards offshore. Upon reaching a position 400 yards from shore the mortar boats lay to but continued their fire on the beaches as the first wave of assault troops passed through. It was now 0934, the time when fire support on the gunboats and mortar boats ceased. Naval gunfire had been lifted when the first wave reached a position 800 yards from shore.
During the initial phase of the assault, the mortar unit expended 3,345 rounds of HE. Because of the offshore wind, only seven rounds of WP were fired, this for ranging in at a position 2,600 yards from shore.
Although the mortar boats stood ready to support the 185th Infantry shortly after 1000, they received no calls for fire because the infantry pushing inland to the Agno River encountered no enemy opposition. The mortar group spent the night anchored just off the mouth of the river, and next morning placed area fire on enemy troops which, according to the shore fire control party, effectively routed the opposition. Some of the LCI(M)s replenished their ammunition from an LST standing by with a reserve of 4.2" shells.
From S plus 1 until S plus 8 (10-17 January), this group, Task Unit 79.8.1, provided twilight smoke concealment and escort service for the Liberty and Victory ships in the San Fabian transport area, a mission which terminated operations of that Task Unit. During this period its mortars fired more than 5,000 rounds of 4.2" ammunition. The 20-mm.guns of the unit expended almost 7,700 rounds during antiaircraft operations
The second group of the mortar boats, the four converted from the ammunition detail, supported I Corps landings east of Dagupan, left of XIV Corps. As in the case of Task Unit 79.8.1, these LCI(M)s provided the ships in its vicinity with the concealment of smoke during the twilight hours when they were so susceptible to enemy air attack. On S plus 3 the group went out of action, its mortar crews returning to their parent unit, the 98th Chemical Mortar Battalion. As far as casualties were concerned, this small unit fared rather badly; on S plus 1 an enemy E-boat torpedoed the radar-equipped flagship with a loss of 2 officers and 2 enlisted men.
Group 78.8.1, the smallest of the three mortar boat units, also supported the I Corps landings near Dagupan. From positions within 3,000 yards of the beach, each of the group's three mortars fired about 100 rounds of high explosives onto road and railroad track just in from the shore. Advancing to within 1,000 yards of the beach, the mortar boats engaged unspecified targets on both the forward and reverse slopes of the low-lying hills, then retired to await call fire from the 98th Chemical Mortar Battalion. No enemy fire was received on the beach. On S plus 3, this group shelled a group of enemy and the railroad station south of Damortis
Vice Adm. Thomas C. Kinkaid, in command of the Lingayen landings, was especially pleased with the work of the mortar boats, reporting that they were more effective for beach neutralization than were escort carrier-based planes.
19 February 1945 - Iwo Jima, Bonin Islands, northwest Pacific basinThe success of mortar boats in Pacific assault operations prompted the Navy to increase the number of this type of vessel. Some were acquired and equipped in California, others at Pearl Harbor. The men who were to fire the mortars on these boats were exclusively Navy men, trained in Hawaii by a cadre from the 189th Chemical Mortar Company under the direction of Lt. Col. Joseph E. Atchison. Naturally, the Navy crews had much to learn; many had never seen the mortar before. To some this lack of knowledge meant apprehension of the weapon, to others it meant incorrect employment, with damage and danger as a consequence. There were several example of a second shell being placed in the mortar barrel on top of a misfire and one case where the crew attempted to jam in three rounds. The training in Hawaii, which included two test runs off Kahoolawe, went a long way in correcting these inadequacies.
On 22 January 1945, the fourteen mortar boats left Pearl Harbor for Iwo Jima where they were joined by the LCI(M)s which had seen action at Lingayen Gulf. Four CWS officers from the 189th Chemical Mortar Company accompanied the Pearl Harbor contingent, attached for the operation to the mortar group five units of six boats each.
On the morning of 19 February 1945, the 4th and 5th Marine Divisions landed on the beaches of the island of Iwo Jima in the face of the heaviest enemy beach resistance since Tarawa. The bombardment of the island that preceded the attack was the heaviest of the Pacific war, and one that benefitted from the experiences of the island assaults that had taken place previously. Three of the five mortar units, Numbers 1, 2 and 5, took part in the actual assault phase (3 units x 6 boats x 3 mortars = 54 mortars).
From H-hour minus 35 until H-hour minus 10, the mortars on these vessels expended 3,240 rounds to bombard specific area targets on the slopes of Mount Suribachi, the 550-foot extinct volcano that dominated the southern end of the island. These mortar groups used a maneuver described as Plan Able. In this plan five LCI(M)s of a mortar group moved counterclockwise in an elliptical pattern around the sixth vessel which served as a reference point. Each boat fired only during the period of the run when it was pointed toward the target area. The advantage of this maneuver was the attainment of the high degree of accuracy needed for interdiction fire, accuracy that could not be realized from the decks of shifting boats attempting to maintain a stationary position.
At H-hour, Units 2 and 5 (12 boats x 3 mortars = 36 mortars), proceeding in column, entered the boat lanes from the west, turned shoreward, formed a line parallel with the sixth wave and followed it toward the beaches. Reaching a position 2,000 yards from shore, the mortars began firing at a rate of 6 rounds per minute and at a constant range of 3,200 yards. Stopping 1,000 yards from the beaches, the mortar boats, now 200 yards apart, maintained fire on a line 1,800 yards inland until H plus 60, when they joined Mortar Support Units 3 and 4 in the rear to repair the damage sustained by the mortar mounts and await further assignment. Group 1 (6 boats), still employing the elliptical maneuver of Plan Able, resumed action at H plus 10 with almost four hours of neutralization fire. When this mission terminated, Group 1 joined the other units in the rear, thus marking the end of mortar boat support during the assault landings on Iwo Jima.
After this first day, the LCI(M)s, with but few exceptions, fired only night-time missions of harassment and interdiction. The small size of Iwo Jima, only 7« square miles in area, and its triangular shape made sea support of land operations singularly appropriate. During the first night mortar units 2 and 5, stationed off the east and west coasts of the point of the island tipped by Mount Suribachi, placed fire on the area between the opposing forces to prevent large-scale counterattacks by the enemy. These missions saw the first significant use of white phosphorous as an aid to observation, every fifth round being WP. On subsequent nights, because of heavy counterbattery fire received by the mortar boats, heavier vessels sometimes directly supported them. The destroyer USS Shannon, for example, covered Mortar Unit 2 as the LCI(M) delivered harassing fire on the night of 23 February.
Mortar boat support gradually decreased until 3 March, by which time all these boats had been recalled. About 60,000 rounds of 4.2" ammunition, about 20 percent of which was white phosphorous, had been expended. Rear Admiral Harry W. Hill of Amphibious Group 2 termed the successful use of "mortar gunboats" in the early phases of the assault "one of the outstanding features of the operation." According to CWS sources, the Marine Corps expressed its enthusiasm for massed fire from mortar boats during the early days of the landings.[Vol. III, pp. 530-32]
1 April 1945 - Okinawa, the Ryukyus Islands, northwest Pacific basinAlmost due west and slightly north of Iwo Jima, even closer to the Japanese home island of Kyushu, lies Okinawa. Large scale use of suicide (Kamikaze = Divine Wind) aircraft and torpedo boats were employed against the landing and support forces. Resistance on shore was increasingly determined and suicidal, a harbinger of what to expect in the already scheduled Operations: Coronet against Kyushu, and Olympic against Honshu (the main island).
CWS-trained Navy crewmen manned a total of 60 LCI(M)s 180 4.2" mortars in support of Tenth Army in the Ryukyus Campaign. Six days before the main assault of Okinawa , two 6-boat mortar groups (36 4.2" mortars) supported the diversionary effort against Keramo Retto made by the 77th (New York Statue of Liberty) Infantry Division. On 1 April 1945, the XXIV Army Corps and the III Amphibious Corps successfully carried out the main landings on the western coast of Okinawa. Prior to H-hour on that morning, seven groups of LCI(M)s, each comprised of six boats (7 x 6 x 3 = 126 4.2" mortars) lined up parallel to the beach behind the assault troops. Each LCI(M) carried 1,000 rounds of HE and 200 rounds of WP. Using Plan Baker, the 42 boats moved through a calm sea at about one knot, their 126 mortars opening up at a point 1,600 yards from shore at a rate of 10 rounds per gun per minute. Firing over the heads of advancing troops, the mortars, in less than an hour, placed about 28,000 rounds on a beach area 1,000 feet deep and 5« miles wide. The mortar boats themselves received no enemy fire.
Another group of LCI(M)s supported the 2nd Marine Division's L-Day feint against the southeast coast of Okinawa. Subsequent 77th Division landings at Ie Shima (where the famous WWII correspondent Ernie Pyle was killed) on 16 April received the support of two groups of mortar boats, while three days later a single group fired for the ruse landing made by the same division in southern Okinawa. From 7 May until 27 June, LCI(M)s, in support of Army and Marine troops, shelled the city of Naha and enemy installations in the vicinity of the capital.
The amphibious use of the 4.2-inch mortar was one of the major contributions of the CWS to the Pacific war. The mortar boat proved extremely effective for close support just before, during and immediately after amphibious landings. It was then that the assault troops, running the gauntlet of enemy fire while attempting to secure a foothold on the beach, benefitted from all the support fire that could be provided. The effectiveness of the mortars in this support is best reflected in the steady increase in the number of mortar boats committed to Pacific assault operations. Only four LCI(M)s saw action in the Palau fighting in September 1944. Seven months later a total of sixty supported Tenth Army operations in the Ryukyus. [Vol. III, pp. 532-33]
To offer comment, additions or corrections to this account, send e-mail to the author, Jack Butler, at firstname.lastname@example.org
Note: Two relatively unknown separate chemical mortar companies, the 91st and the 189th, made significant contributions to the successful employment of 4.2-inch Mortar Gunboats. Both companies in Hawaii trained Infantry, Marine, and Navy personnel to deliver effective support to assault troops. With the 4.2-inch mortar no longer a CWS weapon, having gone to the Infantry in the regimental heavy mortar companies and to the Marine Corps, future amphibious training with mortar gunboats may become standard. Perhaps the Navy has or will adopt mortar gunboats as part of its Amphibious Force. The 91st Chemical Mortar Company (Sep) is included in a Presidential Unit Citation awarded to the Sixth Marine Division Reinforced. The 91st was attached to the Marines on Okinawa while the Navy manned the gunboats offshore.
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