Politically Iceland's position in WW2 was complicated. An independent country but sharing a monarch with Denmark, it declared its neutrality. Britain then invaded it in May 1940 which the Govt duly protested. The Prime Minister of Iceland ordered that the population to treat the British with the "politeness due to guests".
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Reykjavik airport (a grass field) was completely inadequate when occupied and had to be reconstructed. It was given concrete runways starting in Oct 1940 but construction conditions were terrible (they had to be built over sunken oil barrels). It was Sept 1941 before it was fit enough to take large aircraft like Wellingtons.
As a result Kaldadarnes was the first airfield to open when the Battles of 98 squadron moved in during Aug 1940, but it was June 1941 before it formally opened as an RAF station w hen the Hudsons of 269 squadron moved in, and July before its 3 runways were completed. It was also prone to winter flooding, the damage from which caused its closure in Nov 1943.
A flying boat base was established at Reykjavik in July 1940 to be used by detachments of Sunderlands from Oban & Sullom Voe, until the whole of 204 squadron arrived and stayed between April & July 1941. A further flying boat base at Akureyri on the north coast was opened in July 1941.
The airfields that eventually formed Keflavik International Airport were constructed by US engineers in 1942/43.
Until 1943 the RAF was short of torpedo bombers. In Sept 1939 there were 2 squadrons of Vildebeests. Beauforts only began to appear in Nov 1939 to replace the Vildebeests, which didn't disappear until April 1940. By mid-1941 there were 5 squadrons to cover everything from the Bay of Biscay to the Norwegian Sea. Such was the shortage of Beauforts in 1942 as units were sent to the Med & Far East that Hampden squadrons had to be transferred from Bomber Command in April 1942 to fill the gaps. It was late 1942 before Torbeaus started to become available.
Sumburgh in the Shetlands to Trondheim is about 500 miles which rules out using obsolete aircraft like the Battle & Henley to attack KM heavy ships based there in the early part of the war.