Name Seaplane Lighter H21

1.      What is the vessel’s ability to demonstrate history in her physical fabric?

Evidence for designs, functions, techniques, processes, styles, customs and habits or uses and associations in relation to events and people.  How early, intact or rare these features are may impact on significance.

SEAPLANE LIGHTER H 21 is now the only surviving substantially complete seaplane lighter. Her structure is unique, particularly the combination of a fast planing hull shape with a semi-submersible docking bay. Some of the equipment used for flooding and blowing her ballast tanks is still in place. Her hull is made of galvanised steel plates riveted or welded together. It was designed so that, at high speed, the bow wave broke sideways, keeping aircraft wings dry. H 21 was of monohull construction with a pointed bow and a single ‘flying-off deck’, of all timber construction, probably pine, with the various sections fastened together with steel bolts and fittings. The deck planking runs fore and aft and consists of 9 inch wide by 2 inch thick plank sections. She remains in her original configuration, being around 90% original, and her condition is described as very good. Old paint and corrosion were removed in 1999, revealing that her original colour was mid green. Many of her original fittings are intact, and the Kingston type valve, used to open the main flooding chambers in the vessel, is still functional despite being badly corroded. As a lighter, H 21 was normally towed by a destroyer and had no means of propelling herself.

2.      What are the vessel’s associational links for which there is no physical evidence?

Associations with people or places.  Off-ship research.

SEAPLANE LIGHTERH 21 was designed by a serving Naval Officer for a specific purpose, which was to extend the range of the successful Felixstowe flying boats by loading them onto a lighter which could be towed  at  high speed to a launch point close to the German coast. Several of the 30 lighters built to this design were used to carry and launch a single high performance fighter aircraft as a defence  against the high flying Zeppelins used by the German Navy for reconnaissance over the North Sea during the First World War.  Lighters were modified during 1918 by being fitted with a temporary wooden flying-off deck. One successful attack was made by Lt Culley and resulted in the destruction of a Zeppelin in 1918. The use of flying-off platforms on cruisers and later on towed lighters, was an attempt, prior to the development of aircraft carriers capable of flying off and landing their aircraft, to provide air defence at the point of need at sea.

There was no direct aviation development of the towed lighters, except that similar emergency measures were introduced in the Second World War to counter the threat posed by the FockeWulf Condors operating over the Atlantic in 1941. Short term defence was provided by fitting merchant ships with catapult-launched Hurricane fighters until cheap escort carriers could be attached to convoys.

3.      How does the vessel’s shape or form combine and contribute to her function?

Overall aesthetic impact of the vessel, her lines, material she was built from and her setting.  Does she remain in her working environment?

Initially conceived as a means of towing a large flying boat at high speed behind a destroyer in the North Sea, SEAPLANE LIGHTER H 21’s broad beamed hull, which could be ballasted down to load and unload the flying boat, was given an underwater shape akin to that of a fast motor boat. The original hull shape was modified as the result of tank tests which showed that when towed behind a destroyer at 30 knots the original hull form would throw up a solid sheet of spray that could damage the wings of the flying boat. As built in 1918 H 21’s shape was ideal for her role. The unique semi-submersible hull form of the lighter, initially the combination of a simple floating dock and a seaworthy hull, has been developed over the years into the highly successful Landing Ship Docks and semi-submersible load carriers of today.  SEAPLANE LIGHTER H21 is now a static exhibit in the Fleet Air Arm Museum.

Source: NHS-UK team, 26 August 2015. 

This statement was developed as part of the Heritage Lottery funded First World War project. http://www.ww1britainssurvivingvessels.org.uk/