Less well known than the larger LSTs of World War II were the 494 Landing Ship, Medium, amphibious-warfare ships of the LSM-1 class, completed between April 1944 and February 1946. Brown Shipbuilding Company of Houston, Texas, built most of the ships, with the remaining constructed by the Dravo Corporation, Western Pipe and Steel, Federal Shipbuilding and Dry Dock, Pullman Standard Car Manufacturing Company, and the Charleston Navy Yard. Four others were completed as salvage tenders ARS(D)-1 to 4, and 60 were converted as LSM(R)s—Landing Ship, Medium (Rocket).
The basic LSM (including LSM-25B, pictured at top) was designated originally the LCT(7) class and was intended to operate with LCI(L) infantry landing ships; the LSMs brought the vehicles and the smaller LCI(L)s to the troops. The 203.5-foot LSM could deliver five medium or three heavy tanks or other combinations of vehicles totaling up to 165 tons to a beachhead or could be used to carry more than 500 tons of cargo on the open vehicle deck on freighting runs. The LSM possessed a range of around 4,900 nautical miles at 12 knots and had a crew of four officers and 54 enlisted. It could also hold 48 troops to operate the vehicle cargo. Armament was limited initially to six single 20-mm guns, but single or twin 40-mm gunmounts were added later to most in a tub atop the abbreviated forecastle.
LSM(R)-188 to 195 (LSM(R)-194 pictured at center) were fitted with 75 Mk 36 4-rail and 30 Mk 30 6-rail launchers for 5-inch artillery rockets, providing an awesome ripple-fired barrage of up to 480 rounds at a time. Unfortunately, the launchers had to be reloaded manually. LSM(R)-196 to 199 had 85 Mk 51 hopper-type launchers that improved the rate of fire somewhat. Both versions of the early LSM(R) design had the rocket launchers placed on a new upper deck that covered the original cargo deck, used for magazines and rocket assembly rooms. An enclosed 5-inch 38-caliber gunmount was placed on the centerline near the stem, and four 4.2-inch mortars were added to complement the already formidable shore-bombardment capability. Two single 40-mm and three single 20-mm cannons defended against aircraft.
LSM(R)-401 to 412 (LSM(R)-401 pictured at bottom)—and the similar LSM- 501 to 536, which had a forecastle and were about three feet longer—were a more sophisticated solution to the shore fire-support problem. The pilothouse was moved to the centerline near the stern with the 5-inch gun before it, while the fixed rail-type rocket launchers were supplanted by ten twin-tube, trainable, and automatically reloadable Mk 102 launchers. The four 4.2-inch mortars were retained, and the antiaircraft armament was enhanced to two twin, director-controlled 40-mm gunmounts and four twin 20-mm mounts. Three of the dozen LSMRs (retyped LFR) were reactivated for service in Vietnam with the Navy’s only post-war attempt at a shore- bombardment ship, Carronade (LFR-1), while the Elk River (IX-501) remains in U.S. Navy use as a barracks barge at San Diego.