US Army Infantry Squad - 12 men: Squad leader (Thompson submachine gun 'SMG', M1 carbine, or M1 Garand rifle), 10 rifleman (M1 Garand rifle), 1 automatic rifleman (BAR). Organized as: Able Team (2 scouts); Baker Team (5 rifleman), Charlie Team (3 rifleman + BAR). One rifleman per platoon would generally carry a bazooka in addition to his personal weapon. There were 3 rifle squads per platoon in a rifle company.
US Airborne Infantry Squad - 12 men: same as infantry squad except that the BAR is replaced by a M1919A1 light machine gun (LMG). Same organization as the regular infantry squad. In practice the organization was flexible to the mission with one or more rifles often replaced by submachine guns and one man in the squad carrying a bazooka (generally one per platoon).
USMC Rifle Squad - 13 men (1944): The marine squad evolved throughout the war, adding additional firepower with each increment until settling on the 13-man configuration in mid 1944. Organized with a squad leader (Thompson SMG), and 3 x 4-man fire teams (3 rifles + 1 BAR each). In addition to the assigned personal weapons, the company commander could allocate 1 demolition pack and 1 flame thrower per squad as well as 1 bazooka per platoon, depending on mission requirements. These weapons would be carried by one of the squad's rifleman in addition to a personal weapon (often an M1 carbine to lighten the load). Since marines were often engaged in close-in fighting, they would frequently scrounge Thompson SMG's to replace rifles when available.
British & Commonwealth Infantry Squad (Section) - 10 men: Section leader (Sten SMG), Assistant Section Leader (rifle), 6 riflemen (rifle), Bren Number 1 (Bren LMG), Bren Number 2 (rifle). British and Commonwealth forces carried the .303 Enfield rifle (bolt action) throughout the war. The basic squad structure remained constant throught different battalion types (e.g., infantry, motorized, parachute), while the Para's were able to add additional Sten guns based on mission requirements. PIAT anti-tank weapons were allocated to squads from the company level as in the US forces.
Germany (Gruppe) – 10/9 men: The basic German squad centered around an MG34 or MG42 general purpose machinegun (GPMG); personal weapons for the gunners were pistols and rifles (generally), squad leader (MP40 SMG), 7 riflemen (Karabiner 98K 'Mauser' bolt action rifle). As the war progressed and manpower losses mounted the Germans were forced to reduce squad size to 9 men (dropping a rifleman). Panzergrenadier squads (halftrack mounted) had 8 dismounts with 2 GPMGs; Fallschirmjager (paratroop) squads were authorized 11 men, also with 2 GPMGs. In 1944 and 1945 many squads were below authorized strength even after replacements.
USSR - 10 men: The basic infantry squad included a squad leader (SMG), assistant leader (rifle), 5 rifleman (rifle), machinegunner (DP light machinegun), assistant gunner (rifle). Like the Germans, the Soviet forces suffered under terrible casualties and were frequently forced to reduce squad size. They also formed SMG squads of 9 or 10 men all armed with the PPsh 41 submachinegun for close-in assault. In some configurations, the SMG squad would be supplemented with an LMG.
Japan - 13 men: The squad consisted of an NCO squad leader, a machinegunner (Type 96 LMG), and 11 riflemen. All carried bolt action rifles (Arisaka) except the machinegunner. The Japanese did not employ submachineguns in any significant numbers.