Question: When was the helmet, that the M63 replaced, patented ?

full_context: Document 1: Hełm wz. 31: The hełm wz. 31 ("helmet, 1931 pattern") was the basic combat helmet of the Polish Army before the outbreak of World War II and during the Invasion of Poland. The helmet became the basic type of combat headgear for Polish military formations in 1930s and during the early stages of World War II. It was also exported to Persia, Albania and Republican Spain. By September 1939 approximately 320,000 copies were delivered to the Polish Army.
Document 2: M63 helmet: The M63 (nicknamed "Staaldak" in Afrikaans) is a combat helmet of South African origin. Based on the French Modèle 1951 helmet, the M63 replaced the British type Brodie helmets during the early 1960s, and saw extensive use during the Rhodesian and Angolan bush wars. It was issued until the 1980s when it was replaced by the M87 kevlar helmet.
Document 3: Adrian helmet: The M15 Adrian helmet (French: "Casque Adrian" ) was a combat helmet issued to the French Army during World War I. It was the first standard helmet of the French Army and was designed when millions of French troops were engaged in trench warfare, and head wounds from the falling shrapnel generated by the new technique of indirect fire became a frequent cause of battlefield casualties. Introduced in 1915, it was the first modern steel helmet and it served as the basic helmet of many armies well into the 1930s. Initially issued to infantry soldiers, in modified form they were also issued to cavalry and tank crews. A subsequent version, the M26, was used during World War II.
Document 4: Pickelhaube: The Pickelhaube (plural "Pickelhauben"; from the German "Pickel", "point" or "pickaxe", and "Haube", "bonnet", a general word for "headgear"), also Pickelhelm, was a spiked helmet worn in the nineteenth and twentieth centuries by German military, firefighters, and police. Although typically associated with the Prussian army who adopted it in 1842-43,
Document 5: Mk III helmet: The Mk III Helmet was a steel military combat helmet first developed for the British Army in 1941 by the Medical Research Council. First worn in combat by British and Canadian troops on D-Day, the Mk III and Mk IV were used alongside the Brodie helmet for the remainder of the Second World War. It is sometimes referred to as the "turtle" helmet by collectors, because of its vague resemblance to a turtle shell, as well as the 1944 pattern helmet.
Document 6: Standard diving dress: Standard diving dress (also known as hard-hat or copper hat equipment, or heavy gear) is a type of diving suit that was formerly used for all underwater work which required more than breath-hold duration, and included marine salvage, civil engineering, pearl shell diving and other commercial diving work, and similar naval diving applications, though has largely been superseded by lighter and more comfortable equipment.
Document 7: Brodie helmet: The Brodie helmet is a steel combat helmet designed and patented in London in 1915 by John Leopold Brodie. In modified form it became the Helmet, steel, Mark I in Britain and the M1917 Helmet in the U.S. Colloquially, it was called the shrapnel helmet, Tommy helmet, tin hat, and in the United States the doughboy helmet. Worn by Australians during WW2 and sometimes known as Panic Hat. It was also known as the dishpan hat, tin pan hat, washbasin, battle bowler (when worn by officers), and Kelly helmet. The US version, the M1917, was copied from the British Mk 1 steel helmet of 1916. The German Army called it the "Salatschüssel" (salad bowl). The term "Brodie" is often mis-used. It is correctly applied only to the original 1915 "Brodie's Steel Helmet, War Office Pattern".
Document 8: Mk 6 helmet: The Mk 6 helmet was the standard combat helmet of the British Armed Forces. The Mk 6 replaced the Mk IV helmet (more correctly titled - Helmet Steel MK IV, General Service). The jump in MK numbers is thought due to the confusion surrounding the MK IV helmet utilising the MK V lining, introduced in 1959. The MK 6, introduced into service from 1985, is designed to accept modern ear protection, Bowman personal radios, and respirators. The helmet is manufactured by NP Aerospace, and is reported to have an "almost unlimited service life" by the manufacturer.
Document 9: M87 kevlar helmet: The M87 is a combat helmet of South African origin manufactured by South African Pith Helmet Industries (S.A.P.H.I) of Rosslyn. The kevlar composite M87 replaced the steel M63 helmet during the late 1980s, and saw extensive use during the South African Border War, which took place from 1966 to 1989 in South-West Africa (Namibia) and Angola. It is the current standard helmet of the South African National Defence Force.
Document 10: Bonnet (headgear): A bonnet is any of a wide variety of headgear for both sexes—more often female—from the Middle Ages to the present. It is impossible to generalize as to the styles for which the word has been used any more than for the hat and cap, but there is for both sexes a tendency to use the word for styles in soft material and lacking a brim. Yet the term has also been used, for example, for steel helmets. This was from Scotland (in 1505), where the term has long been especially popular. "Bonnet" derives from the same word in French, where it originally indicated a type of material. In the 21st century, only a few kinds of headgear are still called bonnets, most commonly those worn by babies and Scottish soldiers. In addition, bonnets are worn by women as a Christian headcovering in some denominations.
Document 11: Modèle 1951 helmet: The Modèle 1951 helmet was a military helmet used by the French military (Army, Navy, Air Force and Gendarmerie), iconic of the Algerian War. It replaced a variety of helmets used during the Second World War, including the Adrian helmet, Modèle 1945 helmet and American-supplied M1 Helmet.
Document 12: Modèle 1978 helmet: The Modèle 1978 helmet is a modern military steel helmet used by the French Army under the "F1" designation and commonly called "heavy helmet" (other nicknames include "locomotive skin cap"). It replaced the Modèle 1951 helmet, and is superseded by the SPECTRA helmet.
Document 13: Iraqi M80 helmet: The Iraqi M80 Helmet is a military helmet made of compressed canvas used by the Iraqi Armed Forces from the early 1980s onwards. They were used in the Iran–Iraq War, The Persian Gulf War/Operation Desert Storm and the 2003 Invasion of Iraq/Operation Iraqi Freedom. These helmets were originally manufactured and designed in South Korea but in 1990 an Iraqi-made version appeared, which is usually fitted with a distinctive rubber rim. Both types of helmet are still in limited service with the Iraqi Security Forces but are being replaced by the American PASGT helmet.
Document 14: SSh-68: The SSh-68, Russian: СШ-68 (стальной шлем образца 1968 года/stalnoy shlyem, or steel helmet) (English: SSh-68 steel helmet model 1968) - is a steel helmet of the Soviet and then Russian Armed Forces. The SSh-68 is further development of combined-arms helmet SSh-60. It differs primarily in its greater strength, greater front slope of the dome and the shorter outer edge. It is usually painted in dark green.
Document 15: Stahlhelm: Stahlhelm (plural "Stahlhelme") is German for "steel helmet". The Imperial German Army began to replace the traditional boiled leather Pickelhaube (spiked combat helmet) with the Stahlhelm during World War I in 1916. The term "Stahlhelm" refers both to a generic steel helmet, and more specifically to the distinctive (and iconic) German design.
ground_truth: 1915