It was, that was partly the reason it didn’t see proper service.
The Martin B-57A was a licenced built E.E. Canberra bomber, which itself started out with a tandem two seat design cockpit (all be it with the bowl canopy that it retained in production bomber and PR variants), however due to radar bombing kit not being available it became a three seater with the pilot under the bowl canopy and the nav/bomb aimer sat side by side behind him.
The B-57 essentialy was a low level interdictor (before the RAF thought of it) and only required one nav who was retained in the aft stb’d position.
The B-57B introduced the excellent tandem seat layout under the large clear canopy, something that E.E. and the RAF should have done while drawing up the Canberra B.(I).8.

Shame that there aren’t more Martin designs about really, the Marlin is my favourite flying boat.