Anderson Bomb Shelters - History

In November 1938, Prime Minister Neville Chamberlain placed Sir John Anderson in charge of Air Raid Precautions. Sir John was a scientist turned politician who led the Ministry of Home Security. He commissioned the engineer William Patterson to design a small and cheap shelter that could be erected in people's gardens.

The first 'Anderson' shelter was erected in a garden in Islington, London on 25 February 1939 and, between then and the outbreak of the war in September, around 1.5 million shelters were distributed to people living in areas expected to be bombed by the Luftwaffe. During the war a further 2.1 million were erected.

Made from six curved sheets bolted together at the top, with steel plates at either end, and measuring 1.95m by 1.35m, the shelter could accommodate four adults and two children. The shelters were half buried in the ground with earth heaped on top.
The shelters were very strong - especially against a compressive force such as from a nearby bomb - because of their corrugation. See below for further information about their strength and durability.

Anderson shelters were effective only if half buried in the ground and covered in a thick layer of earth. They were therefore inherently cold, dark and damp. In low-lying areas the shelters tended to flood, and sleeping was difficult as the shelters did not keep out the sound of the bombings. If there was a toilet at all, it took the form of a bucket in the corner.

Many families tried to brighten their shelters in various ways, and they often grew flowers and vegetables on the roof. One person wrote that "There is more danger of being hit by a vegetable marrow falling off the roof ... than of being hit by a bomb!'

Strength and Durability

Anderson shelters were very strong - especially against a compressive force such as from a nearby bomb - because of their corrugation. It is relatively easy to bend a flat sheet of metal, but corrugated metal can only easily be bent along the lines of corrugation, and not across them. The roofs of the shelters therefore had to be bent into semi-circular shape in factories and, once bent into shape, they resisted any further inward bending. So the whole structure resisted any further distortion.

Also, the front and rear elements of the shelter were not firmly attached to the two sides, so they could to some extent move independently. This flexibility helped to increase the survival prospects of anyone inside the shelter if a bomb dropped nearby.

Anderson shelters were made of steel, which mainly consists of Iron, and so normally rusts quite quickly in the open air. The steel was therefore coated in Zinc which provided very effective protection against rusting. The process of coating steel with Zinc is called galvanisation and the product is called galvanised steel.

Zinc protects against rusting because it reacts more readily with Oxygen (in air) to form Zinc Oxide. This then reacts with water vapour in the air to form Zinc Hydroxide. Then, finally this compound reacts with Carbon Dioxide in the air to form Zinc Carbonate. And the great thing about Zinc Carbonate is that it is impermeable and insoluble, and sticks very firmly to its parent Zinc and to steel. It therefore forms a very strong barrier which resists any further attack on either the steel or the Zinc coating.

Further protection was provided by painting the galvanised steel and/or burying it under plenty of earth. As a result, some Anderson shelters are in pretty good condition over 70 years later.

Emergency Exits

Every shelter kit was held together with bolts and provided with a spanner-tommy bar. After construction, the spanner was kept in the shelter as it might be needed to loosen the clip bolts at the back of the shelter, and so create an emergency exit if the main door was blocked by bomb debris.

Manufacturers' Marks

During your visit you might see if you can spot a faded wartime maker's mark (or utility stamp?) which was imprinted on much corrugated iron produced during the war, perhaps to show that it was price-controlled.

The top line reads BRITISH MAKE but then there is an image of a sheep, above the word MERINO, which is a type of sheep. The bottom line is HO (for Home Office) with a simple image of a crown between the two letters.