The other two services seem to be able to aviate and maintain a professional level of fitness, why do the crabs seem to make it such a drama?
Most of the matelots I met preferred the bar over the gym any time. I also vaguely recall being told there was no RN fitness test a few years or so ago, and that this was a recent innovation. However I imagine swimming may be of some use.
As for the Army, well that's the Army for you!