UDT(Under Water Demolition Team) wears a Reversible T-Shirt during World War II for training. These divers had the job of clearing underwater obstacles for amphibious landings. It was hard training, and these men had to spend a lot of time in the water to get their special diving skills. The yellow side will be used when the standard is not met, while the blue side will be used normally to indicate the wearer's qualifications and status. These Reversible T-shirts were also used in Vietnam and were worn by SEAL(the successor to the UDT) until the 1990s. Later versions were light blue with no threaded cuffs and long sleeves.