No. 76 Special Incendiary Grenade
Encyclopedia
The No. 76 Special Incendiary Grenade also commonly known as the A.W. bomb or SIP Grenade (Self Igniting Phosphorus) was an incendiary grenade based on white phosphorus used during World War II
.
On 29 July 1940, manufacturers Albright & Wilson of Oldbury demonstrated to the Royal Air Force
how their white phosphorus could be used to ignite incendiary bombs. The demonstration involved throwing glass bottles containing a mixture of petrol and phosphorus
at pieces of wood and into a hut. On breaking, the phosphorus was exposed to the air and spontaneously ignited; the petrol also burned resulting in a fierce fire. Because of safety concerns, the RAF was not interested in white phosphorus as a source of ignition, but the idea of a self-igniting petrol bomb took hold. Initially known as an A.W. bomb, it was officially named the No 76 Grenade, but more commonly known as the SIP (Self Igniting Phosphorus) grenade. The perfected list of ingredients was yellow phosphorus
, benzene
, water and a two inch strip of raw rubber
; all in a half-pint bottle sealed with a crown stopper
. Over time, the rubber would slowly dissolve making the contents slightly sticky and the mixture would separate into two layers – this was intentional and the grenade should not be shaken to mix the layers as this would only delay ignition. When thrown against a hard surface, the glass would shatter and the contents would instantly ignite liberating choking fumes of phosphorus pentoxide
and sulphur dioxide as well as producing a great deal of heat.
Strict instructions were issued to store the grenades safely, preferably underwater and certainly never in a house. Mainly issued to the Home Guard
as an anti-tank weapon, it was produced in vast numbers; by August 1941 well over 6,000,000 had been manufactured.
The grenade could either be thrown by hand, or fired from the Northover projector
, a simple mortar
; a stronger container was needed for the latter and the two types were colour-coded. As any breakage of the flask would be dangerous, storage under water was recommended.
There were many who were sceptical about the efficacy of Molotov Cocktails and SIP grenades against the more modern German tanks. Weapon designer Stuart Macrae
witnessed a trial of the SIP grenade at Farnborough
: "There was some concern that, if the tank drivers could not pull up quickly enough and hop out, they were likely to be frizzled to death, but after looking at the bottles they said they would be happy to take a chance." The drivers were proved right, trials on modern British tanks confirmed that Molotov and SIP grenades caused the occupants of the tanks "no inconvenience whatsoever"
The Home Guard
hid caches of these grenades during the war for use in the event of an invasion. Not all locations were officially recorded and some caches were lost. Occasionally, the caches are discovered by builders digging foundations. In all cases, the grenades are still found to be dangerous and typically are destroyed via a controlled explosion.
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
.
On 29 July 1940, manufacturers Albright & Wilson of Oldbury demonstrated to the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
how their white phosphorus could be used to ignite incendiary bombs. The demonstration involved throwing glass bottles containing a mixture of petrol and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
at pieces of wood and into a hut. On breaking, the phosphorus was exposed to the air and spontaneously ignited; the petrol also burned resulting in a fierce fire. Because of safety concerns, the RAF was not interested in white phosphorus as a source of ignition, but the idea of a self-igniting petrol bomb took hold. Initially known as an A.W. bomb, it was officially named the No 76 Grenade, but more commonly known as the SIP (Self Igniting Phosphorus) grenade. The perfected list of ingredients was yellow phosphorus
Allotropes of phosphorus
Elemental phosphorus can exist in several allotropes; the most common of which are white and red solids. Solid violet and black allotropes are also known. Gaseous phosphorus exists as diphosphorus and atomic phosphorus.-White phosphorus:...
, benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
, water and a two inch strip of raw rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
; all in a half-pint bottle sealed with a crown stopper
Crown Cork
The crown cork , the first form of bottle cap, was invented by William Painter in 1891 in Baltimore. The company making it was originally called the Bottle Seal Company, but it changed its name with the almost immediate success of the crown cork to the Crown Cork and Seal Company...
. Over time, the rubber would slowly dissolve making the contents slightly sticky and the mixture would separate into two layers – this was intentional and the grenade should not be shaken to mix the layers as this would only delay ignition. When thrown against a hard surface, the glass would shatter and the contents would instantly ignite liberating choking fumes of phosphorus pentoxide
Phosphorus pentoxide
Phosphorus pentoxide is a chemical compound with molecular formula P4O10 . This white crystalline solid is the anhydride of phosphoric acid. It is a powerful desiccant.-Structure:...
and sulphur dioxide as well as producing a great deal of heat.
Strict instructions were issued to store the grenades safely, preferably underwater and certainly never in a house. Mainly issued to the Home Guard
British Home Guard
The Home Guard was a defence organisation of the British Army during the Second World War...
as an anti-tank weapon, it was produced in vast numbers; by August 1941 well over 6,000,000 had been manufactured.
The grenade could either be thrown by hand, or fired from the Northover projector
Northover projector
The Projector, 2.5 inch—more commonly known as the Northover Projector—was an ad hoc anti-tank weapon used by the British Army and Home Guard during the Second World War...
, a simple mortar
Mortar (weapon)
A mortar is an indirect fire weapon that fires explosive projectiles known as bombs at low velocities, short ranges, and high-arcing ballistic trajectories. It is typically muzzle-loading and has a barrel length less than 15 times its caliber....
; a stronger container was needed for the latter and the two types were colour-coded. As any breakage of the flask would be dangerous, storage under water was recommended.
There were many who were sceptical about the efficacy of Molotov Cocktails and SIP grenades against the more modern German tanks. Weapon designer Stuart Macrae
Stuart Macrae (inventor)
Colonel Robert Stuart Macrae TD was an inventor best known for his work at MD1 during the Second World War, his best known invention being the sticky bomb.Macrae was the author of Winston Chuchill's Toyshop...
witnessed a trial of the SIP grenade at Farnborough
Farnborough Airfield
Farnborough Airport or TAG London Farnborough Airport is an airport situated in Farnborough, Rushmoor, Hampshire, England...
: "There was some concern that, if the tank drivers could not pull up quickly enough and hop out, they were likely to be frizzled to death, but after looking at the bottles they said they would be happy to take a chance." The drivers were proved right, trials on modern British tanks confirmed that Molotov and SIP grenades caused the occupants of the tanks "no inconvenience whatsoever"
The Home Guard
British Home Guard
The Home Guard was a defence organisation of the British Army during the Second World War...
hid caches of these grenades during the war for use in the event of an invasion. Not all locations were officially recorded and some caches were lost. Occasionally, the caches are discovered by builders digging foundations. In all cases, the grenades are still found to be dangerous and typically are destroyed via a controlled explosion.