The Landing Craft Infantry (LCI) were several classes of landing craft used by the Allies to land large numbers of infantry directly onto beaches during World War II. They were developed in response to a British request for seagoing amphibious assault ships capable of carrying and landing substantially more troops than their smaller Landing Craft Assault (LCA). The result was a small steel ship that could land 200 men, traveling from rear bases on its own bottom at a speed of up to 15 knots.

Some 923 were built starting in 1943, serving in both the Pacific and European theaters, including a number that were converted into heavily armed beach assault support ships. The LCI(L) supplemented the small LCAs/LCVPs as a way to get many troops ashore before a dock could be captured or built. As such, they were the largest dedicated beachable infantry landing craft (the larger Landing Ship Infantry (LSI) was a transporter for men and small craft such as the British LCA) in the Allied inventory.

The LCI(L) was designed to carry 200 men at up to 15 knots and be as capable at landing as the LCA. Since a steel hull would be needed and steel was already earmarked for building destroyers at home, the US was approached. There, the plans were developed into the LCI(L), the Landing Craft Infantry (Large).

The original British design was envisioned as being a "one time use" vessel which would simply ferry the troops across the English Channel, and were considered an expendable vessel. As such, no sleeping accommodations were placed in the original design. The infantry were provided benches (similar to those on a ferry) upon which to sit while they were transported across the channel. This was changed shortly after initial use of these ships, when it was discovered that many missions would require overnight accommodations.

The U.S. was able to come up with an easily-built and mass-produced design by using non-traditional shipbuilding facilities and equipment. The U.S. established LCI building yards at ten different locations.

There were 3 major types of LCI(L) which differed mostly by the location of the ramps and by the shape of the conning tower. All of these ships had similar hulls. The hull of all LCI(L) were 158 ft (48 m) long with a 23-foot beam, making them relatively long and narrow.

The 3 major LCI(L) types are normally referred to as: a) Square Conning tower, Side Ramp (the original style); b) Round Conn, Side Ramp; and c) Round Conn, Bow Ramp.

On LCI(L)1-349 class, (Square Conn, Side Ramps) the deck was wider than the prow and two gangways on either side of the bow led onto a pair of ramps that were lowered, and down which troops would disembark. The LCI 350 class had a single enclosed bow ramp with two bow doors that swung open. The reason for moving the ramp to the inside was to provide some protection for the troops as they disembarked to the beach, if only by concealing them from enemy sight. Also, the low, squared-off conning tower was upgraded on later models (LCI(L)350 and higher) with a taller, round conning tower which afforded slightly more visibility from the bridge.

The steepness and narrowness of either type of bow ramps made the LCI impractical for landing troops as part of an initial assault against a defended beach, and they were sometimes reserved for the follow-up waves, after the LCA or LCPL boats had landed. However, they were included in the first waves at numerous invasions such as Anzio, Normandy, Southern France, Elba, Saipan, the Philippines, Iwo Jima, Guam, and Okinawa.

The first LCI(L)s entered service in 1943 chiefly with the Royal Navy (RN) and United States Navy. Early models were capable of carrying 180 troops, this was increased to 210 later. Craft in service with the two navies had some variation according to national preferences. Some 923 LCI were built in ten American shipyards and 211 provided under lend-lease to the Royal Navy. In Royal Navy service they were known as "HM LCI(L)-(pennant number)". During Project Hula, the United States in June and July 1945 secretly transferred 30 LCI(L)s to the Soviet Navy, which designated the type as desantiye suda ("landing ship") or DS; they saw action against the Japanese after the Soviet Union entered the war against Japan in August 1945, and five – DS-1 (ex-USS LCI(L)-672), DS-5 (ex-USS LCI(L)-525), DS-9 (ex-USS LCI(L)-554), DS-43 (ex-USS LCI(L)-943), and DS-47 (ex-USS LCI(L)-671) – out of 16 involved were lost on 18 August 1945 during the landings on Shumshu. The Soviet Union eventually returned 15 of the surviving LCI(L)s to the United States, all in 1955.^[6]

In use, the LCI fleet was used for numerous missions. One important use was for smoke laying to obscure the invading fleet from enemy artillery or aircraft. Still others were used to provide close-in gunfire support to the troops who had just landed on the beach. In one such episode, eight LCI(G) were used two days prior to the invasion of Iwo Jima to protect Underwater Demolition Team insertion and beach mapping teams. They were mistaken by the Japanese defenders as the main invasion, and were fired upon by numerous previously hidden large caliber coastal defense artillery, (up to 8 inch). Three of these LCI(G) were sunk and all were damaged. Lt.(j.g) Rufus G. Herring (CO LCI Force) received the Medal of Honor for this action.

In another instance, Lt. Alec Guinness RNVR made numerous trips as the Commanding Officer of HMS LCI(L)-124 delivering troops to the beach near Cape Passero lighthouse on 9 July 1943 during the Allied invasion of Sicily. He missed the call from his commander to delay the landing and went on to land 25 minutes ahead of the rest of the LCI Flotilla. As he was returning from the beach empty, he was rebuked by his Flotilla Commander, who thought he was deserting from the fight, when he informed the Commander he was on his way back to get more troops after having already landed once.^[7]

Most LCI(L)s were struck from service by both the Royal Navy and the U.S. Navy in 1946, and were put into reserve, sold, scrapped, or used as target ships. In addition to the 30 LCI(L)s, transferred to the Soviet Union in Project Hula, the United States also transferred LCI(L)s to Argentina (15), the Republic of China (13), France (14), Indonesia (7), Chile (6), the Dominican Republic (3), the Philippines (3), Israel (2), Thailand (2), and the Republic of Korea (1).

In February 1949, the U.S. reclassified the remaining LCIs as "Landing Ship Infantry" (LSI). Landing Ship Infantry was a term that had been used during the war since around 1941 by the British for various vessels such as converted ferries and passenger ships that could carry 800–1,800 troops close to shore, the final transfer being by smaller boats.

As with the Landing craft tank, the LCI(L) was used as the basis of a number of conversions into specialist vessels.

The Landing Craft Support (Large) or "LCS(L) Mark 3" was built by the United States. These ships were built on a standard LCI hull, but were modified to add gunfire support equipment and accommodation. They were armed with a single 3"/50 caliber gun and/or two twin 40 mm cannon and numerous 20 mm cannon. These ships were prevalent in most major Pacific Theater invasions beginning in late 1944. The type was reclassified as Landing Ship Support, Large (LSSL) in 1949. One hundred and thirty of this type were built.

Several LCIs survive and are available to be seen by the public.

The LCI(L)-713, (a round conn, bow ramp) is located in Portland, Oregon near the I-5 Bridge over the Columbia River. It is currently owned and being restored by a non-profit 501c3 group, the "Amphibious Forces Memorial Museum".^[14] Built in 1944 in Neponset, Massachusetts, the ship was transferred to the Pacific Theatre where it saw action in making two assault landings: Zamboanga, Philippines in March 1945 and Brunei Bay, Borneo in June 1945 (as part of the Battle of North Borneo). Purchased as war surplus initially for use as a log hauling tugboat, the engines were removed and it was relegated to a floating storage hulk in Stevenson WA until the late 1950s when it was abandoned and sank into the river mud on the shore of the Columbia river. In the late 1970s the ship was refloated and restoration began on the ship. LCI(L)713 has changed ownership until finally sold to the AFMM in 2003. The LCI(L) 713 has been continually restored with the goal of becoming a historically correct operating museum vessel.

Another survivor is LCI(L)-1091 (also a round conn, bow ramp). Moored in Eureka, California, she is owned and operated by the Humboldt Bay Air & Sea Museum.^[15] The ship was used in the Korean War in 1951-1953 as an "Infectious Disease Control Ship". Her interior was modified to accommodate a larger crew that included ten Medical Doctors and Lab Technicians. In the late 1950s the ship was sold as surplus for use as an Alaskan fishing vessel. 30 years later, the 1091 was purchased and brought to Eureka, California, in the 1990s by Ralph "Doc" Davis for use as a private fishing vessel. Doc Davis sold the ship to the museum, headed by Mr Leroy Marsh, and they are working together to restore the LCI-1091 to an operating museum vessel.

Several former LCI hulls were obtained and modified for use as sightseeing vessels after World War II by the New York City "Circle Line".^[16] The Circle Line 7 (ex-LCI-191), Circle Line 8 (ex-LCI 179) are all now retired. Circle Line X is currently on active duty with Circle Line 42nd Street on New York City's Pier 83.

Several other LCI hulls have been located around the world. The Argentine Navy has at least three, which were being used as of 1998. The ex LCI(L)-653, renamed Husky II, was used as a pilot boat and then a fisheries tender in Alaska before being broken up at Homer, Alaska in 2010. Three derelict LCI hulls remain at Staten Island, New York, in the Witte Marine salvage yard.

Only one LCS(L) Mk.3, the former LCS-102, still survives in original configuration. She is moored at Mare Island, California, where she is being restored to her World War II appearance by volunteers.^[17][18]

• List of United States Navy Landing Craft Infantry (LCI)
• List of United States Navy amphibious warfare ships