The first of the Greek Pusher Seaplanes flew in February 1914, successfully passing trials in March, with first deliveries in May and all six delivered by the outbreak of the First World War. Two more identical trainers were purchased by the Royal Naval Air Service, again for use as trainers, these being delivered in May. While the Greek machines performed well, despite the limited facilities available at their base at Eleusina, with at first no workshops or hangars available, the two British aircraft were less successful, with their engines proving unreliable, and were withdrawn by February 1915.
In March 1914, the Greeks placed an order for six more pusher seaplanes, the Sopwith S PG N, which were similar to their previous aircraft, but rather than being dual control trainers, were to be armed with a machine gun in the nose, and powered by a Gnome Monosoupape rotary engine. At least five of these aircraft were taken over by the Royal Navy at the outbreak of war, but again proved unsuccessful in British Service, with at least two being modified as landplanes. They remained in service until July 1915.
The Royal Navy ordered six modified landplane based on the S PG N in July 1914, the Sopwith Gunbus or Admiralty Type 806, to be powered by 110 hp (82 kW) Sunbeam water-cooled V8 engines and armed with a machine gun. The first one flew on 6 October 1914, and was found to be underpowered, so was fitted with a 150 hp (112 kW) Sunbeam. A further 30 aircraft were ordered from Robey & Co. Ltd. of Lincoln in early 1915, these being fitted with a modified nacelle, with the pilot sitting in the forward cockpit rather than the gunner, and fitted for bombing. Only 17 of these aircraft were completed, with the remaining 13 delivered as spare parts.
The Sunbeam-powered Gunbuses saw limited operational use, with one aircraft being on the strength of the RNAS squadron at Dunkirk led by Commander Charles Samson in February 1915, with Samson commenting that the Sopwith required "a lot of work on it to make it safe to fly". The Gunbuses were used mainly as trainers, being used by the RNAS at Hendon, and remaining in service until the winter of 1915-16.
The name Gunbus came from the Royal Flying Corps (RFC) pilot's slang term for an aeroplane - a bus - and was also used in the name of the Vickers Gunbus.