US Navy Explosive Ordnance Disposal dive equipment
A frogman's breathing set should:[opinion]
Be as silent as possible in use.
Have a full face diving mask:
To let frogmen communicate underwater.
Be less easily knocked off underwater.
Be much less easily lost if the frogman becomes unconscious underwater.
Be securely fastened, see here about full-face diving masks. It should have as little as possible (e.g., an excessively bulky or projecting set/air valve) that can catch on things or that an attacker could easily grasp.
Be a dull color to avoid being seen from out of the water. Many are black, but the Russian IDA71's backpack box is mostly dark green. No large bright-colored badges or manufacturer's logos.
Contain as little iron or steel as possible, to avoid detection by magnetic sensors. This is also useful when the frogmen have to remove or defuse mines underwater.
Be as light and agile as possible, as far as is compatible with an adequate dive duration:
Be well streamlined, and as small and light as possible for the dive duration. With a combat diver this may mean removing safety features such as an open-circuit bailout that would add bulk. Long trailing hoses (e.g., regulator hoses) are easily fouled and or pulled at and add to drag. If an underwater fight, or a quick need to escape, develops, agility and lack of cumbersomeness could be vital. This applies to:
Streamlining in straight swimming, as he may have to swim fast and far.