High quality Reproduction 504th Parachute Infantry Regiment pocket patch.
Pocket patches were applied to M41 jackets, jump jackets or flight jackets, usually on the left breast. However, this varied a bit from unit to unit- so if historical accuracy is important, it's best to research the specific unit. Machine-embroidered on twill or wool, or hand-sewn bullion.
It is historically incorrect to wear these in the field or "in combat". Pocket patches were only for casual or "walk out" uniforms.