Complex sentence: Rebreathers would not have been used by UDT operators at anytime during World War II. The OSS Maritime Units did have Lambertsen rigs which were an early type of rebreather, but the UDT operators relied on their ability to breath hold.
Split into simpler sentences: Rebreathers would not have been used by UDT operators at anytime during WW2. The UDT operators relied on their ability to breath hold.