Armstrong Whitworth Siskin Mk.IV/Mk.V

The development of the Siskin Mk.V started before the Mk.IIIA and was an improved version of the previous Mk.II. It had the shorter upper-wing span and broader chord lower-wing and parallel struts of the Mk.II together with a redesigned vertical tail surfaces, a forward fuselage with rounded sides and was powered by a 385hp Armstrong-Siddeley Jaguar III engine.
It was armed with two Vickers 0.303 machine-guns placed at the sides of the frontern part of the fuselage.

When it was presented, the Romanian government showed interest on it and ordered 70 examples. The production of those examples started in 1925 but in March of that year one Siskin V used as demonstrator that was piloted by a Romanian pilot, crashed, and the order was cancelled, with at least 10 examples being completed but without deliveries having been made.
It's known that at least two Siskin V were flown with civilian registrations.
The Siskin Mk.IV was an ad-hoc civil racing version made for the 1925 King's cup race and it looked similar to the Mk.V. It won that race.

Sources:
1. https://en.wikipedia.org/wiki/Armstrong_Whitworth_Siskin
2. Salamander Books - The Complete Book of Fighters

Armstrong Whitworth Siskin Mk.III/Mk.IIIA - British Users

In  1922 the 14/22 specification was issued by the Air Ministry for an all-metal single-seat high performance airplane and one Armstrong Siddeley Jaguar powered prototype was ordered from Armstrong Whitworth.

Apart from re-engining the airplane, in order to fit the Jaguar IV engine, Major Green, the original designer of the Siskin, redesigned it with an all-metal fuselage, as the Siskin III.
It was praised by the Air Ministry, which placed a contract for three production aircraft on 13th October 1922, with a further six ordered on  26th January 1923, being one of them a prototype for a two-seat variant.
The Siskin Mk.III flew for the first time on 7th May 1923 and the first deliveries to the RAF took place in January 1924. It was the first all-metal fighter to serve with the Royal Air Force.

The Siskin Mk.III was powered by a 385hp Armstrong Siddeley Jaguar IV radial engine and was armed with two Vickers 0.303 machine-guns placed at the sides of the frontern part of the fuselage.

The main production variant, the Siskin Mk.IIIA, was ordered in 1926 and, initially it was powered by a regular Jaguar IV engine, but it was re-engined with the supercharged version of that same engine, the Jaguar IVA. The supercharged engine concept was a novel idea for the time and had little impact on the performance below the 3050m, but it improved the performance and climb rate above that height.
It was powered by a single Armstrong Siddeley Jaguar IVA engine, delivering also 385hp of power, was armed with two Vickers 0.303 machine guns, this time buried in the frontal part of the fuselage, instead of the sides, like the regular Mk.III had and it could carry up to four 9Kg small bombs under the wings.
As Armstrong Whitworth was busy manufacturing the Armstrong Whitworth Atlas, many of the later production of the Siskin was contracted to other firms like Blackburn, Bristol, Gloster and Vickers.

Sources:
1. https://en.wikipedia.org/wiki/Armstrong_Whitworth_Siskin
2. Salamander Books - The Complete Book of Fighters

Armstrong Whitworth Siskin Mk.IIIA - Foreign Users

The Armstrong Whitworth Siskin was a British single-seat biplane fighter of the 1920s that was used by some foreign users, Canada and Estonia, more precisely.

The Royal Canadian Air Force used the Sisikin from 1926 until 1939. They were sent in 1926 to be tested under winter flying conditions, equipped with skis instead of regular wheels and the original modified type was piloted by Clenell H. Dickins. It was considered as a very advanced airplanes fighter for the time and the RCAF eventually bought them and they were assigned to the Flight No.1 based at Camp Borden and Trenton, in Ontario.
In 1937 the Flight was reformed and it became the No.1 Squadron Royal Canadian Air Force and was moved from Trenton and Borden to Calgary, in Alberta.

It remained active with that unit until 1939 when, due to the outbreak of the war, it was replaced by the more modern Hawker Hurricane.
It also equipped the first RCAF flight demonstration unit, the Siskin Air Demonstration team, nicknamed 'The Siskins'.

Apparently, Estonia also purchased some Siskins, not the fighter ones, but the trainer one, the Siskin IIIDC, which was a two-seater. However further details about those airplanes under Estonian command are unknown.

Sources:
1. https://en.wikipedia.org/wiki/Armstrong_Whitworth_Siskin
2. http://www.canadianwings.com/Aircraft/aircraftDetail.php?SISKIN-6
3. Salamander Books - The Complete Book of Fighters.

Armstrong Whitworth Siskin - Prototype and Mk.II

The Armstrong Whitworth Siskin was a British single-seat bipane fighter of the 1920s and was one of the first airplanes to enter service with the Royal Air Force after the end of the World War I.

The first prototype, was built by Siddeley-Deasy, company that was soon incorporated into Armstrong Whitworth, and was designed by Major F.M. Green who was the former chief engineer of the Royal Aircraft Factory. Initally it was Siddeley-Deasy's candidate for the Type1 fighter for a single-seat fighter powered by the ABC Dragonfly radial engine.
The S.R.2 Siskin was a single-bay biplane made out of wood and fabric. Wings were of unequal span and it was fitted with a distinctive fixed landing gear equipped with long oleo strut shock absorbers carrying the axle which was connected to the Radius Rods by a pair of V-struts. The engine was fitted inside a streamlined cowling to reduce drag with each cylinder coming out through special holes designed for them. It was armed with a pair of 0,303 Vickers machine-guns placed at the sides of the frontern part of the airplane.

It flew first in May 1919 and the Dragonfly engine delivered 270hp of power, instead of the theorical 320hp and, in spite of all the expectations put on the Dragonfly engine, it proved to be a disaster as it was underpowered and it was very unreliable being very prone to overheating and causing an untolerable amount of vibration. Even if those were serious issues, the Siskin proved to handle better than it's Dragonfly powered competitors.

The second version, the Mk.II, derived directly from the Siddeley-Deasy S.R.2 which was adquired by Armstrong Whitworth after Siddeley-Deasy closed down their aviation department. It reatined the basic features of it's predecessor but, on the other hand, it was radically redesigned structurally. It embodied fuselage and wing spars of high-tensile steel tubing and strip. The engine was switched from the ABC Dragonfly to the newly built Armstrong-Siddeley Jaguar 14-cylinder two-row that could deliver 325hp of power. It was armed, as the Siddeley-Deasy Siskin, with a pair of 0,303 Vickers machine-guns.
It appeared in August 1922 and the second one was completed in October 1923 but it failed to attract production order so it was sold to the Swedish Aircraft Company of the Signal Corps (the forerunner of the Swedish air force) where it was fitted with skis to make it able to land under winter conditions.

Sources:
1. https://en.wikipedia.org/wiki/Armstrong_Whitworth_Siskin
2. Salamander Books - The Complete Book of FIghters