HM Motor Gun Boat 501
HM Motor Gun Boat 501 was a motor gunboat operated by Royal Navy Coastal Forces of the [Royal Navy|Coastal Forces] during the Second [World War]. The design, prepared by Bill Holt of the DNC's Boat Section, was unusual for a British light coastal forces' boat at the time in that it was of composite construction, whereas most MTBs and Motor Launches were entirely wooden-hulled. MGB 501's frames and various internal members were steel, with layers of diagonal wooden planking forming the exterior skin of the hull and wood for the remaining decks & bulkheads.
She was initially designed as a combined anti-submarine boat and motor torpedo boat, but was completed as a Motor Gun Boat. Based on the lessons of combat experience with the early MA/SBs following their conversion to MGBs, MGB 501's initial designed gun armament, which would have included a 2-pdr Rolls gun, was replaced with a suite that would have provided greater reliability and volume of fire in battle. Retaining her 21-inch torpedo tubes, she therefore completed for service as a combined motor gun & torpedo boat whilst being designated purely as an MGB.