The Mouse was a low-wing monoplane touring aircraft, powered by a 130 hp (97 kW) de Havilland Gipsy Major piston engine.

The Comper Mouse was a low-wing cantilever monoplane that was promoted as being suitable for use by private owners, for air taxi services, or other forms of commercial operation.

This roof could be opened mid-flight to aid in visibility when approaching an airport under unfavourable weather conditions or in advance of performing a forced landing in which the aircraft potentially turning over was a risk.

[4] The Mouse was furnished with several noteworthy features for the era; one of the more difficult engineering challenges was its adoption of a retractable landing gear arrangement, which Comper pursued a patent for.

[2] Each wheel (and its associated axle) was carried upon a series of welded square steel tubes; the manner in which these were arranged, placing bronze blocks against rubber pads, permitted it to slide up and down.

[2] This mechanism was claimed to be relatively easy to work, each unit being controlled by an individual lever and both levels being located between the front seats in close proximity to one another.

Furthermore, a red warning lamp, which automatically lit up if the throttle was pulled back when the wheels were in still retracted, was present amongst the cockpit instrumentation.

[5] The tail unit was fitted with a wooden stabilizer that was mounted on top of the fuselage; it had routed spars and solid spruce diagonal bracing.

[5] It was powered by a single de Havilland Gipsy Major piston engine that was installed upon a welded steel-tube mounting just forward of a fireproof bulkhead.

[7][8][9] On 13–14 July 1934, the Mouse (registered G-ACIX) was flown by E.H. Newman in handicapped heats for the King's Cup Race at Hatfield Aerodrome under poor weather conditions.