The mine flotilla consisted of a mine planter, a distribution box boat (DB boat, also known as a L-boat after the numerical designation on the side of the boat), and two to four yawls. There were rarely enough mine planters for one to be assigned to each harbor that had mines. Often one or two mine planters were assigned to a major harbor. They would be called on to perform service in other harbors or in the laying and maintenance of the military underwater cable systems. Smaller harbors without assigned mine planters would be visited by a planter for practice, and during wartime after it had performed its duty at its primary station. Many harbor defenses used vessels that were jury-rigged to serve as makeshift mine planters and DB boats due to the lack of a sufficient number of actual army mine planters.
Army mine planters were custom built after 1904. They had wide decks to hold assembled mines, and the necessary booms and davits for loading the assembled mines from the wharf and planting the mines out in the channel.
The four mine planters ordered in 1904 were 150 ft. in length, 32 ft. beam, 14 ft. draft and 447 tons in displacement.
The 1940 series of mine planters were 188 ft. in length, 37 ft. beam, 12 ft. 6 in. draft and displaced 1,320 tons.
The ships had a wartime crew of two officers, 6 warrant officers, and 41 men.
Usually the fleet would plant one group of mines at a time.
Distribution box boats were smaller boats that held the distribution box while it was being attached to the cables as the mines were being planted. The DB boat had a large boom to hoist an assembled distribution box over the bow and lower it into the water.
The mine yawls were typical small craft which were used to ferry ropes, cables, etc., from the mine planter to the DB boat or shore as needed.