Question: Peter Isaacson served in a branch of the military in World War II that was originally formed in what year?

Context paragraphs:
44th Battalion (Australia): The 44th Battalion was an infantry unit of the Australian Army.  Originally formed in 1916 for overseas service during World War I, the battalion fought in the trenches along the Western Front in France and Belgium between late 1916 and 1918, before disbanding at the conclusion of hostilities.  During the inter-war years, the 44th became part of the part-time Citizens Force, based in Western Australia.  During World War II, it undertook garrison duties in Australia but was not deployed overseas to fight.  In the post-World War II period the 44th was amalgamated with the 11th Battalion, before being subsumed into the Royal Western Australia Regiment in 1960.

1st (United Kingdom) Division: The 1st (United Kingdom) Division, formerly the 1st Armoured Division, is a division of the British Army, currently the only British division to be stationed in Germany.  Originally formed in November 1937 as the Mobile Division, it saw extensive service during World War II and was disbanded afterwards; reconstituted in 1976, it remains in service.  It should not be confused with the 1st Infantry Division, which saw service in World War II as a separate formation.

3rd Battalion, 3rd Marines: 3rd Battalion, 3rd Marines, abbreviated as (3/3), is an infantry battalion of the United States Marine Corps, based out of Kāne'ohe, Hawai'i.  Known as either "Trinity" or "America's Battalion", the unit falls under the command of the 3rd Marine Regiment of the 3rd Marine Division.  The unit consists of approximately 1124 U.S. Marines and United States Navy sailors.  Like most battalions of the U.S. Marine Corps, 3rd Battalion, 3rd Marines is made up of three rifle companies (India, Kilo, and Lima), a Headquarters and Services (H&S) company, and a weapons company.  The battalion was originally formed at Marine Corps Base Camp Lejeune, North Carolina in 1942 and saw action on both Bougainville and Guam during World War II, where it was awarded the first of its Presidential Unit Citations for "gallantry, determination, and esprit de corps in accomplishing its mission under extremely difficult and hazardous conditions"; and the first of its Navy Unit Commendations for "outstanding service".  Marines in the battalion were also awarded one Medal of Honor and seven Navy Crosses during the war.  Following World War II, 3rd Battalion was disbanded until 1951, when it was reformed in California.  The battalion was alerted for possible deployment during the 1956 Suez War and the 1958 intervention in Lebanon.  In 1965, the Marines of 3rd Battalion were deployed to the Vietnam War and participated in Operation Starlite, the first major Marine engagement of that conflict.  The battalion continued to see major action through Vietnam and was rotated back to the United States in 1969.  Famous alumni from its time in Vietnam include Corporal Robert Emmett O'Malley, the first Marine in Vietnam to be awarded the Medal of Honor, Oliver North, and John Ripley.  Around the end of the Vietnam War, the Battalion was deactivated for a second time in 1974.

Royal Australian Air Force: The Royal Australian Air Force (RAAF), formed March 1921, is the aerial warfare branch of the Australian Defence Force.  It directly continues the traditions of the Australian Flying Corps (AFC), formed on 22 October 1912.  The RAAF provides support across a spectrum of operations such as air superiority, precision strikes, intelligence, surveillance and reconnaissance, air mobility, and humanitarian support.

II Corps (United States): The II Corps was a corps-sized formation of the United States Army that was active in both World War I and World War II.  It was originally formed and fought on the Western Front during World War I and was also the first American formation of any size to see combat in North Africa or Europe during World War II.

Assam Rifles: The Assam Rifles is the oldest paramilitary force of India.  The unit can trace its lineage back to a paramilitary police force that was formed under the British in 1835 called "Cachar Levy".  Since then the Assam Rifles have undergone a number of name changes—the Assam Frontier Police (1883), the Assam Military Police (1891) and Eastern Bengal and Assam Military Police (1913), before finally becoming the Assam Rifles in 1917.  Over the course of its history, the Assam Rifles and its predecessor units have served in a number of roles, conflicts and theatres including World War I where they served in Europe and the Middle East, and World War II where they served mainly in Burma.  In the post World War II period the Assam Rifles has expanded greatly as has its role.  There are currently 46 battalions of Assam Rifles with a sanctioned strength of 63,747 personnel.  It is under the control of the Indian Ministry of Home Affairs (MHA) and they perform many roles including the provision of internal security under the control of the army through the conduct of counter insurgency and border security operations, provision of aid to the civil power in times of emergency, and the provision of communications, medical assistance and education in remote areas.  In times of war they can also be used as a combat force to secure rear areas if needed.  Since 2002 it has been guarding the Indo–Myanmar barrier as per the government policy "one border one force".

38th Battalion (Australia): The 38th Battalion was an infantry battalion of the Australian Army.  Originally formed in 1916 for service overseas during World War I as part of the Australian Imperial Force (AIF), the battalion was recruited from the state of Victoria and formed part of the 10th Brigade, 3rd Division.  It served throughout the war on the Western Front before being disbanded in 1919.  During the inter-war years, the battalion was re-raised as a part-time military unit and during the World War II undertook garrison duties in Australia, but did not see combat.  After the war, it was re-formed in Victoria and was eventually subsumed into the Royal Victoria Regiment, with its honours and traditions being preserved by the 8th/7th Battalion, Royal Victoria Regiment.

4th Brigade (Australia): The 4th Brigade is a brigade-level formation of the Australian Army.  Originally formed in September 1914 for service during World War I, elements of the brigade served at Gallipoli and in the trenches on the Western Front before being disbanded in 1919.  In 1921, the brigade was re-raised as a unit of Australia's part-time military forces, based in the state of Victoria.  During World War II the brigade served in the New Guinea and New Britain campaigns. Following the war, the brigade formed part of the 3rd Division, however, it was later reallocated to the 2nd Division, where it serves as a Reserve combined-arms formation including units and personnel from all corps of the Army including armoured, infantry, artillery, engineers, signals and ordnance.

Siberian Military District: The Siberian Military District was a Military district of the Russian Ground Forces.  The district was originally formed as a military district of the Russian Empire in 1864.  In 1924 it was reformed in the Red Army.  After the end of World War II the district was split into the Western and Eastern Siberian Military Districts.  In 1956 the district was reformed.  In 2010 it was divided between the two newly formed Central and Eastern Military Districts.

Peter Isaacson: Peter Stuart Isaacson, AM, DFC, AFC, DFM (31 July 1920 – 7 April 2017) was an Australian publisher and decorated military pilot.  He was the owner of Peter Isaacson Publications, publisher of various trade journals and suburban newspapers including the "Southern Cross" and the "Sunday Observer" in Melbourne.  During World War II, he served in the Royal Australian Air Force (RAAF) as a pilot with RAF Bomber Command and was awarded the Distinguished Flying Cross, the Air Force Cross and the Distinguished Flying Medal.

Supporting paragraphs: Peter Isaacson Royal Australian Air Force
Answer: 1921