Prior to WWII, the Marines did not have a specific uniform for use in combat, wearing either their winter or summer service uniforms depending upon the climate. The Army, unlike the Marines, had a specific "field" uniform (Class C) Both forces used fatigue or utility uniforms made of blue denim, meant to be worn during menial non-combat work or training to avoid unnecessarily soiling the service uniform. The M1941 utility uniform was introduced on November 7, 1941 to replace the blue denim work uniform. It was made of sage-green herringbone twill fabric, and was meant to be worn over the service uniform during work or training. The shirt had a breast pocket on the left side, printed with the "Eagle, Globe, and Anchor", as well as two more pockets on the lower front. The pants had two patch pockets on the seat, as well as one on each side. Marines soon began to eschew wearing their service uniforms altogether in favor of the M1941s.

The Army, along with the Marines, tested a one-piece camouflage coverall ("Suit, One-Piece, Jungle") made of heavy herringbone twill fabric early in the Pacific war (late 1942 to early 1943) It had a "brown" (tan fabric with brown spots) and "green" (straw-colored fabric with dark brown and green spots) side and was fully reversible. The uniform was meant to be worn without any kind of undergarments. It was little-used and quickly discarded by most men after it was realized the one-piece construction made it hard to take off in a hurry; soldiers and Marines in the Pacific were often confronted with bouts of sudden diarrhea (the suit didn't even have a drop seat!) from tropical diseases and swarms of biting insects. It provided adequate protection from thorny plants, but was also very heavy when wet. In late 1943, the Marines introduced the redesigned Pattern 1942 camouflage HBT uniform. It sported the same colors as the one-piece coverall but was in two pieces, pants and a shirt. It also came with a reversible camouflage helmet cover. Some patterns of the helmet cover had slits for the insertion of scrim (foliage, sticks, or fabric) The uniform was worn by Marines on Bougainville, Tarawa, and New Georgia, but stopped being worn by the end of these campaigns as it was realized the camouflage effect of spots only worked effectively when the user was standing or sitting still. Most Marines who were issued with the uniform kept the helmet cover; this is where we get this image of the WWII-era Marine from.

The United States Army adopted a variant of the P1942 camouflage uniform for very limited use in Europe to satisfy agitators in the Corps of Engineers. It had various modifications deemed necessary including a gas flap and internal suspenders. Due to the suspenders, the uniform was fixed "green side" out. The uniform was issued to units of the 2nd Armored Division (17th Armored Engineer Battalion and 41st Armored Infantry Regiment) and the 2nd and 30th Infantry Divisions in July 1944. It was not officially withdrawn, but gradually fell out of use by September 1944.

The P1944 HBT camouflage uniform first saw action on Saipan, and then very sparingly afterwards for the rest of the war. It had several modifications when compared to the P1942; instead of two patch pockets on the seat of the pants, there was now a single large one, similar to a pouch. The side pockets had small flaps with snaps to cover them.