The Northern Bombing Group consisted of United States Navy and United States Marine Corps squadrons conducting strategic bombing of German U-boat bases along the Belgian coast during World War I.
 The first United States military unit sent to Europe was the First Aeronautic Detachment of seven naval officers and 122 enlisted men who arrived in France on 5 June 1917.
 These men became the nucleus of the United States Naval Forces in Europe.
 They formulated a strategic bombing plan approved by the Secretary of the Navy on 30 April 1918, but chronic difficulties in obtaining aircraft prevented establishment of an effective bombing campaign before the war ended six months later.
The 1st Battalion was an infantry battalion of the Australian Army.
 Although its numerical name was designated during the First World War, the 1st Battalion can trace its lineage back to 1854, when a unit of the Volunteer Rifles was raised in Sydney, New South Wales.
 This unit has since been redesignated a number of times, but through its links with the units of the colonial NSW defence force, the battalion's history includes services in Sudan and South Africa.
 During the First World War, the 1st Battalion was raised for overseas service in 1914 as part of the First Australian Imperial Force.
 Attached to the 1st Brigade, the battalion served in Egypt initially before taking part in the fighting in Gallipoli against the Turks.
 Later the battalion was sent to the Western Front where it fought in the trenches in France and Belgium as part of the Australian Corps.
 Following the end of the war the battalion was disbanded in 1919.
"Lions led by donkeys" is a phrase popularly used to describe the British infantry of World War I and to blame the generals who led them.
 The contention is that the brave soldiers (lions) were sent to their deaths by incompetent and indifferent leaders (donkeys).
 The phrase was the source of the title of one of the most scathing examinations of British First World War generals, The Donkeys—a study of Western Front offensives—by politician and writer of military histories Alan Clark.
 The book was representative of much of the First World War history produced in the 1960s and was not outside the mainstream—Basil Liddell Hart vetted Clark's drafts—and helped to form a popular view of the First World War (in the English-speaking world) in the decades that followed.
 However, the work's viewpoint of incompetent military leaders was never accepted by some mainstream historians, and both the book and its viewpoint have been subject to attempts at revisionism.
No. 5 Airfield Construction Squadron (5ACS) was a Royal Australian Air Force (RAAF) construction squadron.
 The unit was first formed in July 1942 and served in the New Guinea Campaign and Borneo Campaign during World War II.
 The squadron was one of only a few RAAF airfield construction units to be retained at the end of the war, and formed part of Australia's contribution to the occupation of Japan from 1945 until it was disbanded in June 1949.
 5ACS was re-raised in August 1951 and worked on several RAAF airfields in Australia.
 In addition, it also provided small detachments of engineers to support RAAF deployments to South Vietnam and Thailand during the Vietnam War.
 The squadron was the RAAF's only airfield construction unit from 1961 onward, and was disbanded in December 1974.
The 246th (Nova Scotia Highlanders) Battalion, CEF was a unit in the Canadian Expeditionary Force during the First World War.
 Based in Halifax, Nova Scotia, the unit began recruiting in the summer of 1916 throughout the province of Nova Scotia.
 The unit sent two drafts to England in April and June 1917, both of which were absorbed into the 17th Reserve Battalion, CEF upon arrival.
 The 246th (Nova Scotia Highlanders) Battalion, CEF had one Officer Commanding: Lieut-Col.
 N. H. Parsons.
The Western Front was the main theatre of war during the First World War.
 Following the outbreak of war in August 1914, the German Army opened the Western Front by invading Luxembourg and Belgium, then gaining military control of important industrial regions in France.
 The tide of the advance was dramatically turned with the Battle of the Marne.
 Following the Race to the Sea, both sides dug in along a meandering line of fortified trenches, stretching from the North Sea to the Swiss frontier with France, which changed little except during early 1917 and in 1918.
The Western Desert Campaign (Desert War), took place in the deserts of Egypt and Libya and was the main theatre in the North African Campaign during the Second World War.
 The campaign began in September 1940 with the Italian invasion of Egypt; Operation Compass, a British five-day raid in December 1940, led to the destruction of the Italian 10th Army.
 Benito Mussolini sought help from Adolf Hitler, who responded with a small German force sent to Tripoli under Directive 22 (11 January).
 The German "Afrika Korps" ("Generalleutnant" Erwin Rommel) was under nominal Italian command but Italian dependency on Nazi Germany made it the dominant partner.
The Slovene Partisans (formally National Liberation Army and Partisan Detachments of Slovenia) were part of Europe's most effective anti-Nazi resistance movement led by Yugoslav revolutionary communists during World War II, the Yugoslav Partisans.
 Since a quarter of Slovene ethnic territory and approximately 327,000 out of total population of 1.3 million Slovenes were subjected to forced Italianization since the end of the First World War, the objective of the movement was the establishment of the state of Slovenes that would include majority of Slovenes within a socialist Yugoslav federation in the post-War period.
Although considerable conflict took place outside Europe, the European theatre was the main theatre of operations during World War I and was where the war began and ended.
 During the four years of conflict, battle was joined by armies of unprecedented size equipped with new mechanized technologies, leaving millions dead or wounded.
The 1st Durham Engineers, later Durham Fortress Engineers, was a Volunteer unit of the British Army's Royal Engineers.
 First founded in 1868 it was sometimes united with the Tyne Electrical Engineers, at other times it formed an independent unit.
 Although its main role was defence of the North East Coast of England, the unit sent detachments on active service to the Suakin Expedition, the Second Boer War, and the Western Front and Italy during the First World War.

Question: What unit sent detachments to the main theatre of war during the First World War?
Answer: The 1st Durham Engineers