INTRODUCTION
The Major Caliber Lightweight Gun Mount (MCLGM) is a result of Navy and Marine Corps efforts beginning in 1960 to provide the fleet with the first major caliber gun mount to be designed since the end of World War II. This mount would provide firepower necessary to support troops ashore at ranges well beyond that of 5"0 guns and would provide greatly increased firepower for the fleet, particularly for smaller ships. A 175mm/60 caliber mount was specified by Reference 1 because of the potential advantages of achieving commonality in ammunition with the Army 175mm gun. Northern Ordnance Division of FMC Corporation at Minneapolis (NOD/fmc) was awarded the contract to design and develop the mount. A prototype was fabricated and subjected to testing at NOD/fmc, including a 50,000 cycle life and reliability test, on the loading system. The mount was disassembled and delivered to the Naval Weapons Laboratory, Dahlgren. Virginia in August 1970 where it was reassemble checked, proof-fired and evaluated to verify that contract requirements were met.
The Army, however, developed only one type of projectile for an anticipated family of ammunition; terminated plans for future ammunition development; planned the phaseout o! the 175mm gun; and commenced development of an "up-gunned" 8-inch howitzer. Accordingly, the original SOR, Reference 1, was revised and superseded by Reference 2 in October 1969. The MCLGM was directed to be an 8-inch gun in production using the basic design established in the development of the 175mm prototype To meet these new requirements, a program was authorized in February 1971 to convert the prototype MCLGM from its 175mm/60 configuration to an 8"/:55 Thus, the Naval Weapons Laboratory, by Reference 3, was assigned the responsibility to effect this conversion and to evaluate the 8"/55 MCLGM MARK 71 MOD 0.
The oscillating assembly was returned to NOD/fmc in March 1971 for modification of the recoil and counterrecoil system to handle the increased loads when firing 8".0 MARK 25 projectiles. Since the cartridge case remained the same for both the 175mm and 8*0 applications, only minor modifications were required to the ammunition handling system to accommodate the heavier projectile. These were accomplished on the mount without removing it from its permanent emplacement. Two 175mm liners were converted to an 8".0 by Watervhct Arsenal. A four caliber extension was added to one liner so that it might be used in the mount, the second liner was converted to an 8"/51 caliber test gun for interior ballistic development programs. Two new 8*/55 caliber liners were also machined from new forgings. The converted oscillating assembly was returned to NWL in August 1971 and the mount was reassembled. The 8".0 MCLGM prototype mount was proofed with the EX 28 MOD 0 liner (with the extension) on 3 September 1971.
