The 10th and 11th Marine Regiments were actually the respective Marine Division's Artillery Regiments. For the Guadacanal landings the Regiments' Heavy Battalions (105mm howitzers) were left behind along with the Divisions' MT Battalions through lack of sufficient shipping space.
Each Marine Artillery Regiment prior to 1943 consisted of three battalions of 75mm Howitzers and one of 105mm Howitzers. For the Guadacanal landings each of the assaulting Marine Infantry Battalion was assigned a battery of six guns (N.B. The Heavy Batteries having just four guns ).
Sources:
- First Offensive-The Marine Campign for Guadacanal by Henry I Shaw Jr (Marine Corps Historical Centre, 1992)
- US Marine Corps 1941-45 by Gordon Rottman (Osprey Publishing, 1995)