For jobs on the special operations/special warfare side (SEAL, SWCC, diver/EOD), you must swim a stroke that is considered an underwater recovery stroke, such as the breaststroke, elementary side ...

Butterfly is a difficult stroke to swim as it needs both stamina and style. The movements you need to make, however, are not difficult because you will have done many of them before in other strokes.

If you do not do everything in the right order your stroke will have no style ... things spend a few sessions practicing them and then have a look at intermediate butterfly.