A Periscoping Pillbox

A Pickett-Hamilton fort is a type of hardened field fortification built in Britain during the invasion crisis of 1940–1941.  The Pickett-Hamilton fort was designed to be lowered into the ground while it was not in use, as such it would be inconspicuous and would not interfere with the passage of taxiing aircraft or other vehicles. The fort could be raised to about 2 feet 6 inches (0.76 m) above ground level where it would be a physical impediment to aircraft [including soldiers parachuting into an airfield] and vehicles and from where a small crew could fire with rifles or light machine guns.

                                            Pickett-Hamilton fort at Southsea

Development

The open spaces of airfields were very vulnerable to attack by airborne troops and it was felt that it was particularly important to defend them effectively. However, conventional defences such as pillboxes and trenches could not be installed without danger to friendly aircraft. At this time a number of private companies contacted the government with their own design ideas.

The Pickett-Hamilton fort was designed by Francis Norman Pickett and Donald St Aubyn Hamilton. Pickett (1887–1957) was an engineer. He graduated from London University in 1907, and from 1918 to 1931 he was Proprietor of the firm of F. N. Pickett et Fils, engaged on the demolition of ammunition. This business encountered many difficulties but Pickett made a great deal of money before the company eventually failed.  Pickett spent much of the early '20s involved in motor racing. He subsequently became Managing Director of Kaycee, Ltd., in 1931–35, of Consolidated Rubber Manufacturers, Ltd., in 1935–38, and of Ocean Salts (Products), Ltd., in 1938. Hamilton (1907–1956) was an architect based in London. Later, as part of Donald Hamilton, Wakeford & Partners, he designed many buildings in London and southern England.

A friend of Norman Pickett, racing driver Donald Campbell, allowed his workshops to be used to build the prototypes. In early 1940, Campbell attended the operational trials of the prototype at RAF Andover.

Winston Churchill wrote to General Ismay on 12 July 1940 saying: "I saw these pillboxes for the first time when I visited Langley last week. This appears to afford an admirable means of anti-parachute defence and it should surely be widely adopted. Let me have a plan." This pillbox was adopted by the Air Ministry and became known as the Pickett-Hamilton fort

Design

The most common version of the Pickett-Hamilton fort consists of two cylinders of pre-cast concrete each with one end closed. The slightly smaller of the two cylinders slides into the larger and they are kept apart by small guard rollers on the moving part that engaged with grooves. The structure is buried so that the overhanging top of the smaller cylinder lies flush with the ground. Closed in this position the pillbox is inconspicuous and allows aircraft and other vehicles to safely drive straight over it.

The interior is accessed via a small hatch and rungs built into the structure. To bring it into action a lifting mechanism was used to raise the inner cylinder by about 2 feet 6 inches (0.76 m) thereby revealing three embrasures. A crew of two men could then operate the fort as a pillbox.

Initially, the lifting mechanism consisted of a standard 8-ton aeroplane jack that took three minutes to raise the fort. This was soon replaced with a pneumatic ram that was based on a system originally intended for agricultural use. The pneumatic system operated with compressed air stored in cylinders: this allowed the fort to be raised and lowered quickly when speed was essential. A hand pump was also provided to raise the fort for daily maintenance or as a backup method.

An alternative design used counterbalance weights to raise the fort. This allowed the fort to be raised by the physical strength of the garrison. This design had two access hatches and, with a slightly larger underground chamber and the elimination of the central pneumatic ram the fort could have a crew of four men. Under consideration in late 1940, this alternative design was not used in significant numbers and only about a dozen were installed.

The cost of construction was about £240 (equivalent to £11,800 in 2017

https://en.wikipedia.org/wiki/Pickett-Hamilton_fort