German submarine "U-5269" was a Type XXVIIB "Seehund" midget submarine which bears one of the highest registry numbers of the Kriegsmarine to be issued to a submarine during World War II.
 "U-5269" was not, however, the last German submarine commissioned (that boat was "U-4712") but was issued a higher registry since contracted boats were frequently commissioned out of order due to scheduling and construction conflicts.
The Type 032 midget submarine and its experimental version Type 032-1 belongs to a family of midget sub developed by the People's Liberation Army Navy (PLAN) in the late 1950s, and it was one of the first submarine indigenously developed in the People's Republic of China (PRC).
 However, due to the political turmoil in China at the time, Type 032 series was cancelled after only a single unit was completed.
The HA.
 19 (also known as Japanese Midget Submarine "C" by the US Navy) is a historic Imperial Japanese Navy "Type A Kō-hyōteki"-class midget submarine that was part of the Japanese attack on Pearl Harbor on 7 December 1941.
 This submarine was ordered to enter Pearl Harbor then attack the American warships with its torpedoes and then be scuttled with explosives next to a warship.
 However, she did not enter the harbor, and was grounded and captured.
 The submarine was eventually put on display near the submarine squadron at Naval Station Key West, Florida, then moved to the nearby Key West Lighthouse and Military Museum.
 "HA.
 19" is now displayed at the National Museum of the Pacific War in Fredericksburg, Texas.
Forel (Russian: Форель , German: "Forelle" - Trout) was a midget submarine designed by Raimondo Lorenzo D’Equevilley-Montjustin and built by Krupp in Kiel, Germany.
 The design was an experimental design built as a private venture by Krupp in hopes of attracting a contract from the Imperial German Navy.
 Although the design proved moderately successful, the submarine did not attract German naval attention.
 She was purchased by the Imperial Russian Navy in 1904 and served with the IRN until she was lost in a diving accident in 1910.
 She had the distinction of being the first submarine to have been built in Germany, preceding SM U-1.
 "Forel" was succeeded in service by the "Krab" class (one ship).
Kraka, or "UC2 Kraka" was an amateur-built midget submarine completed in 2005, the first diesel-electric amateur sub in Denmark.
 It was built by Peter Madsen, Claus Nørregaard and several other people.
 The overall length was 12.6 meters and it displaced 6 tonnes.
 The propulsion was diesel-electric with a 16 hp diesel engine and an 8 hp electric motor.
 Kraka can be seen at Denmark's Technical Museum in Elsinore (aka Helsingør).
In late May and early June 1942, during World War II, submarines belonging to the Imperial Japanese Navy made a series of attacks on the cities of Sydney and Newcastle in New South Wales, Australia.
 On the night of 31 May – 1 June, three "Ko-hyoteki"-class midget submarines, each with a two-member crew, entered Sydney Harbour, avoided the partially constructed Sydney Harbour anti-submarine boom net, and attempted to sink Allied warships.
 Two of the midget submarines were detected and attacked before they could successfully engage any Allied vessels, and the crews scuttled their boats and killed themselves.
 These submarines were later recovered by the Allies.
 The third submarine attempted to torpedo the heavy cruiser USS "Chicago" , but instead sank the converted ferry HMAS "Kuttabul", killing 21 sailors.
 This midget submarine's fate was unknown until 2006, when amateur scuba divers discovered the wreck off Sydney's northern beaches.
The Argonaut Junior was the first successful submarine built by engineer Simon Lake.
 Her main attribute, like that of the sub built by Lake in 1897, Argonaut (submarine), was an air lock.
 Her dimensions were length 14ft, beam 4 ft, depth 5 ft. Different sources incorrectly identify "Argonaut No 1", and "Argonaut No 2" as the name of this vessel.
 "Argonaut No 1" was built in 1897 and is 36 feet in length, "Argonaut No 2" was a reconstruction of "Argonaut No 1" finishing in 1900 with a length of 60 feet and significantly different profile.
UC3 Nautilus is a privately built Danish midget submarine.
 It was built over a three-year period as an art project by Peter Madsen and a group of volunteers, and cost approximately US$200,000 to build (1.5 million DKK).
 The submarine was Madsen's third submarine design, and at the time of launch on 3 May 2008, was the largest privately built submarine in the world.
Peter Langkjær Madsen (] ; born 12 January 1971) is a Danish aerospace engineering enthusiast, "art engineer", submarine builder, entrepreneur, co-founder of the non-profit organization Copenhagen Suborbitals, and founder and CEO of RML Spacelab ApS.
Rocket Madsen Space Lab (often called RML Spacelab) was a laboratory established by Peter Madsen on 16 July 2014 in Copenhagen, after he left Copenhagen Suborbitals.

Question: What was the length of the midget submarine built in 2005 by the founder and CEO of RML Spacelab ApS?
Answer: 12.6 meters