Service of the piece 105-mm Howitzer, M 2, truck-drawn - USA Field Artillery Field Manual, FM 6-75 Service of the piece 8-inch Howitzer M 1 - USA Field Artillery Field Manual, FM 6-91 Advanced map and aerial photograph reading - USA Basic Field Manual, FM 21-26 Service of the piece : 105-MM howitzer self-propelled - USA Armored Force Field Manual, FM 17-63 Service of the piece : 155-mm gun M 1 - USA Field Artillery Field Manual, FM 6-90