10/31/2011. Remarks by Johan Visschedijk: "Formed in 1926, the Swedish AF drew the specification for its fourth fighter, intended for the defense of coastal fortifications and Navy ships, in 1927. The specification stipulated as power plant the 420 hp Bristol Jupiter IV nine-cylinder air-cooled radial engine, and that the aircraft would have to be float-equipped. Designated J 4 (J=Jagt, Fighter) two specimen of the Swedish first and only maritime fighter were ordered from Heinkel in September 1927.

The Heinkel H.D.19 W (H.D.= Heinkel Doppeldecker, Heinkel biplane; W = Wasser, water) was first flown at Warnemünde in July 1928. While test flown both aircraft wore the Swedish s/n 280 and 281, but not the Swedish national markings. The aircraft were delivered to Sweden in August 1928 and were in service at F 2 Wing at Hägernäs some months later.

In the mean time Heinkels subsidiary Svenska Aero AB at Lidingö, an island in the inner Stockholm archipelago, presented a quotation to the Swedish AF and in October 1928 Svenska Aero received an order for four additional aircraft under the s/n 282 to 285. The first was delivered in May 1929, the last the following September.

The floats proved to be limiting the aircrafts operation and performance, however, the HD 19 had been prepared in its basic design for alternative landing gear, so the aircraft was often flown with a wheels landing gear or on skis. All aircraft were equipped with 0.315 in (8.00 mm) KSP m/22 machine guns, two fixed (forward) and one flexible (in back seat).

In November 1934 three J 4 aircraft remained (s/n 281, 282, 285), these were transferred to F 1 Wing at Västerås and were deregulated to secondary duties. The last J 4 (s/n 281) was withdrawn from use on August 31, 1937, after a total flight time of 812 hours."