The SDU-5/E strobe light was issued with various aircrew survival vests and life preservers.
It was waterproof and produced an intermittent flash of light visible for beyond five miles. Army and Special Forces recon units also used the SDU-5/E at night to mark their position on the ground to circling planes.
In such cases the strobe was placed inside the barrel of an M79 grenade launcher so that only those above the end of the barrel would see the flash, thus preventing the enemy from seeing the exact position of the team.
MODEL NO: SDU5/E
SERIAL NO: 6900
TYPE: LIGHT, MARKER, DISTRESS
CONT NO: DSA-400-73-C-4325
NEO-FLASHER NO HOLLYWOOD, CAL
These items were left by the Americans in Vietnam after the war.