While there is no universally agreed-upon definition of the difference between and Submersible and a Submarine, DEEP’s favoured explanation is that the former necessitates the use of a host-vessel – typically a support ship or, sometimes, a submarine – from which to begin and end its journey; whereas a Submarine is able to complete a mission, in its entirety, without the requirement for a secondary vessel to be within the vicinity providing either operational or logistical support.

As such, and as a statement of DEEP’s intent with Subs, DEEP prefers the term ‘Submarines’.