The Heinkel HD 23 was a carrier-borne fighter biplane designed in Germany at Heinkel Flugzeugwerke in the 1920s, for export to Japan.
 Two examples were delivered to Aichi as pattern aircraft in 1927.
 Aichi added rudimentary flotation capability and built two further examples as the Type H Carrier Fighter, but full-scale production was not started.
The Heinkel HD 36 was a trainer developed in Germany in the 1920s at the request of the Swedish Air Force, which was in search of a new trainer aircraft.
 The newly formed air force had previously evaluated the HD 35, found it to be underpowered, and asked Heinkel to address this problem.
 Heinkel's response was a development of the HD 35 modified to use the Mercedes D.III engine instead.
 The HD 36 also dispensed with the third cockpit that had been a feature of the HD 35 and HD 21 before it, but otherwise the design was largely the same.
 The single example built by Heinkel was tested by the Air Force, and found still not quite satisfactory, was modified by CFM (the Air Force workshops) until the problems had been largely eliminated.
 Once this had happened, CFM built two batches of 10 aircraft, delivering them in 1928 and 1930 as the Sk 6.
The Heinkel HD 55 was a biplane flying boat produced in Germany in the early 1930s for use as a reconnaissance aircraft aboard Soviet warships.
 The design was based on the HD 15 mail plane of 1927 and was a conventional design for its time, with equal span, unstaggered wings, and an engine mounted tractor-wise on struts above the pilot's open cockpit.
 A second open cockpit was added on the rear fuselage to provide a position for a tail gunner.
The Heinkel HD 26 was a reconnaissance seaplane developed in Germany during the 1920s for production in Japan.
 It was intended as a smaller, single-seat counterpart to the HD 25, to provide a spotter aircraft for warships, to take off from a short ramp.
 The HD 26 was a conventional biplane with staggered wings, twin float undercarriage, and an open cockpit.
An aircraft carrier is a warship that serves as a seagoing airbase, equipped with a full-length flight deck and facilities for carrying, arming, deploying, and recovering aircraft.
 Typically, it is the capital ship of a fleet, as it allows a naval force to project air power worldwide without depending on local bases for staging aircraft operations.
 Aircraft carriers are expensive to build and are critical assets.
 Carriers have evolved since their inception in the early twentieth century from wooden vessels used to deploy balloons to nuclear-powered warships that carry numerous fighter planes, strike aircraft, helicopters, and other types of aircraft.
 While it is possible to launch heavier aircraft such as fixed-wing gunships and bombers (it has been done) from aircraft carriers, it is virtually impossible to land them.
The Heinkel HD 40 was a special-purpose cargo aircraft developed in Germany in the 1920s to distribute the Berlin newspaper "B.Z.".
 The success of Heinkel's previous design for the publisher, the HD 39, led to the order of a similar aircraft with greater capacity, and Heinkel responded with a machine of similar layout, but considerably enlarged.
 Like the HD 39, it was a conventional single-bay biplane with staggered wings of unequal span, and a fuselage that nearly filled the interplane gap.
 The pilot sat in an open cockpit, and the undercarriage was of fixed, tailskid type with divided main units.
 The wings were of wooden construction, while the fuselage was built from welded steel tube skinned in plywood.
The Heinkel HD 39 was a special-purpose cargo aircraft developed in Germany in the 1920s to distribute the Berlin newspaper "B.Z.".
 It was a conventional single-bay biplane with staggered wings of equal span, and a fuselage that nearly filled the interplane gap.
 The pilot sat in an open cockpit, and the undercarriage was of fixed, tailskid type with divided main units.
 The sole example of the type was built after Ernst Heinkel found out, by chance, that "B.Z." required such an aircraft and had ordered two machines from Albatros.
 Heinkel convinced publisher Ullstein-Verlag to purchase a third aircraft from his firm.
The Heinkel HD 56 was a reconnaissance seaplane developed in Germany in 1929 to operate from warships of the Imperial Japanese Navy, which designated it the Type 90-1 Reconnaissance Seaplane or E3A.
 It was a conventional single-bay biplane with staggered wings braced by N-type interplane struts.
 The pilot and gunner sat in tandem, open cockpits. Heinkel designed the aircraft at the request of Aichi, in order to submit it as their entry in an IJN competition to select such an aircraft.
 Heinkel built a single HD 56 prototype that was evaluated against the Nakajima Type 90-2 Reconnaissance Seaplane and the Kawanishi Type 90-3 Reconnaissance Seaplane.
 The Heinkel design announced the winner in 1931, on the condition that Aichi would address some shortcomings, particularly a lack of range.
 Refined versions of the "losing" Nakajima and Kawanishi designs would eventually see production and - in the case of the Nakajima design - in far greater numbers.
The Heinkel HD 32 was a trainer developed in Germany in the 1920s, a derivative of the HD 21.
 Like that aircraft, it was a conventional, single-bay biplane, but had only two cockpits rather than the three that the HD 21 had.
 The other significant change was the use of a Siemens radial engine in place of the inline units that powered most of the HD 21 family.
The Heinkel HD 38 was a fighter aircraft developed in Germany in the late 1920s.
 It was a compact, single-bay biplane with staggered wings of unequal span, braced with N-type interplane struts, a refined version of the HD 37 that had been evaluated and rejected by the "Reichswehr" for use at the secret training facility at Lipetsk.
 The HD 38 was designed in the hope of capturing a different niche - that of a seaplane fighter, and was designed with a twin pontoon undercarriage that could be quickly removed and replaced with wheels.
 It was accepted in this role, but did not serve in it for long before being relegated to general training duties.
 Even then, it was not long before Germany abandoned the Lipetsk base to the Soviet Union.

Question: Heinkel HD 23 was a type of plane that was held on the craft that were first developed when?
Answer: early twentieth century