What is this structure and aircraft? It is Real Photograph number 188.
Judging by the “FB” on the tail, the aircraft is most probably a Franco-British Aviation FBA 17 designed by Louis Schrek.
That looks like a fixed test article representing an early version of the catapults used to launch flying boats and float planes (like the Kingfisher) from battleships before carriers were integrated into the fleets.
See this article for (one of) the last iterations of this kind of catapult.
Aircraft launched this way were recovered by landing alongside and winching back aboard. Once the jet era began, no competitive fighter aircraft could be launched with this small a catapult (nor did any exist with floats or as flying boats -- there were a couple such designs, but they went nowhere), and aircraft carriers had much stronger catapults mounted in the flight deck (a practice that continues to the present), obsoleting this launching method and indeed launching fixed-wing aircraft from non-carrier ships until VTOL jets became common.
The aircraft on the cradle looks very much like an (Aeromarine 40) (I now believe this is correctly the FBA 17 as given in the other answer). Correct tail shape, wing type, extended trailing edge ailerons, and inline or V engine. That would date this photo after the Armstice, likely during the early 1920s.
Note that the aircraft shown on the catapult is essentially a late WWI design -- fabric and wires on a wood or steel tube frame, the hull a little sturdier than the wings in terms of covering. Even if designed to be armed, aircraft from that period always look fragile compared to even the biplane fighters of the 1930s.