Complex sentence: A two-storied hangar, each level high and long, was built on top of the remaining hull; the upper hangar level opened on to a short'flying-off deck', below and forward of the main flight deck.
Split into simpler sentences: A two-storey hangar, each level high and long, was built on top of the remaining hull. The upper hangar level opened onto a short flying-off deck, below and forward of the main flight deck.