CT (also expressed RCT; RLT) = Combat Team (Regimental Combat Team; Regimental Landing Team). A marine regiment with sufficient service and support to enable it to operate independently of division (or brigade) headquarters when necessary. Essentially a task force. Attached service and support typically consisted of a battalion of artillery, a company each of tanks, medical, engineers, pioneers, etc., and a platoon each of reconnaissance, communications, etc. RCT 1 = 1st Marines (Reinforced) and so forth.
LT (also expressed BLT) = Landing Team (Battalion Landing Team). Battalion-size counterpart of the above - service and support typically consisting of a battery of artillery, a platoon each of tanks, engineers, etc. and a section each of reconnaissance, communications, etc. Battalions are designated in fraction form: 1/1 = 1st Battalion, 1st Marines; BLT 1/1 = Battalion Landing Team (built around) 1st Battalion, 1st Marines.