[6] The design incorporated two 238 horsepower (177 kW) geared Armstrong Siddeley Lynx IV radial engines driving wooden tractor propellers.

According to a 1929 article in Flight, the fuel load of 135 imperial gallons (610 L; 162 US gal) of petrol was estimated as providing the aircraft with a range of around 300 miles (480 km).

Mitchell designed them to have a thick high-lift aerofoil section—he selected the Göttingen 387 design—so as to enable the fully-loaded Seamew to fly at low speeds without stalling.

The following year, the Supermarine S.5, Nanok, and Sparrow II projects, as well as the need to make modifications to the Southampton, all caused further delays, so that work on the Seamew only began in October 1926.

It emerged that the hand-starter gear was prone to failure, and when the aircraft was full loaded, the propellers sustained damage when they hit sea spray during take-off.

As the aircraft proved to be nose-heavy, which prevented it from gaining altitude at its best climbing speed, Supermarine modified the tailplane by fitting balanced rudders.

[13] This incident, as well as the potential expense involved in making new mainplane fittings and rebuilding the airframe, led to both aircraft being scrapped that year.