Eight Heinkel HD 24s (HD = Heinkel Doppeldecker), Sk 4 in the Air Force, was ordered in the first half of 1926 by the MFV (the Navy aviation), just before the forming of the Swedish Air Force. The aircraft was designed as a naval aviation trainer, but the floats could be replaced by wheel landing gear or skis. The eight Sk 4s were all based at the naval aviation Wing F 2 at Hägernäs.

Heinkel had originally built two HD 24s for the competition ”Seeflugwettbewerb” in 1926. Further aircraft were built for the German Airline Pilot School (DVS). The Swedish Sk 4s were ordered from Heinkel’s Swedish subsidiary Svenska Aero AB. 

However, the first two Sk 4s were manufactured at Heinkel’s Warnemünde works as pattern aircraft for the rest of the series. The two aircraft were approved by the Air Force in November 1926. Some months later, they were given the Air Force numbers 201 and 202. The six aircraft built in Sweden were approved in July 1927 - November 1928 (Air Force numbers 203-208). 

The story of the engines installed at the HD 24s is somewhat complex. The six first aircraft (201-206) were fitted with Mercedes engines of 180 hp. These engines were unfortunately not very reliable. Therefore, the 207 and 208 got Junkers Jumo L 25 engines. These engines delivered 280 hp (100 hp more than the Mercedes engines). The 207 and 208 got the subdesignation Sk 4A. After some time, also the 203, 204 and 206 got the L 25 engine and got their designation changed to Sk 4A. Aircraft 201, 202 and 205 also got their original Mercedes engines replaced, but this time to the Armstrong Siddeley Puma (240 hp). New designation Sk 4B.
Heinkel HD 24 in Sweden, built by Svenska Aero AB
Type Werk.Nr Registration History
Sk 4 / Sk 4A 36 203 Built 1927. Delivered to Wing F2, accepted 1927-07-28. Crashed 1929-04-12 at Hägernäsviken. The crew was killed. Scrapped 1929-05-14. Total flying time 268,55 hours
Sk 4 / Sk 4A 37 204, 2504 Built 1927. Delivered to Wing F2, accepted 1927-07-02. Crashed 1934-01-25 at CFV, Västerås. The pilot was wounded. Scrapped 1934-05-04. Total flying time 643,40 hours
Sk 4 / Sk 4B 38
 205, 2505 Built 1927. Delivered to Wing F2, accepted 1927-08-06.  Scrapped 1937-02-02. Total flying time 553,50 hours
Sk 4 / Sk 4A
 39 206, 2506, 2-06 Built 1927. Delivered to Wing F2, accepted 1927-09-09. Crashed 1931-01-19, repaired. Scrapped 1937-02-02. Total flying time 614,05 hours
Sk 4 / Sk 4A 50 207 Built 1928. Delivered to Wing F2, accepted 1928-11-09. Emergency landing east of  Stockholm  1929-08-14, a destroyer tried to tow the plane but the towrope broke and the plane Went down. Discarded 1929-08-27. Total flying time 122 hours
51 208, 2508, 2-08 Built 1928. Delivered to Wing F2, accepted 1928-11-09. . Discarded 1929-08-27. Total flying time 581,55 hours
Heinkel HD 24 in Sweden, built by Heinkel
Type Werk.Nr Registration History
Sk 4 / Sk 4B 253 101, 201, 2501, 2-09 Built 1926. Delivered to Wing F2, accepted 1926-11-17.  Discarded 1937-02-02. Total flying time 822,55 hours
Sk 4 / Sk 4B 254 102, 202, 2502 Built 1926. Delivered to Wing F2, accepted 1926-11-17. Major crash 1928-02, rebuilt at CFV. Transferred to Wing F4 in 1933, back to F2 1937 Scrapped  1939-09-08. Total flying time 622 hours