The truth is that the Germans tried hard to capture Murmansk in 1941. When that failed, they concentrated on attempting to destroy the port from the air and to sink the fabled Arctic convoys, which carried vast quantities of stores from Britain – not just the USA – to the USSR from August 1941 until the end of the war.
In June 1941 a determined German effort (Operation Silver Fox) was made to seize Murmansk with mixed German and Finnish forces. However, the offensive quickly ran out of steam and by the time the winter arrived the Germans were heavily outnumbered and had been successfully countered by superior Soviet forces.
On 22 September 1941, after repeated attempts to advance past the Litsa river, the German offensive was broken off and no further attempt to seize Murmansk made. The main German effort now focused on attempting to destroy the convoys bringing in war materials from both the UK and the USA, and by aerial attack.
The reasons for German failure included vast distances; the tyrannies of the arctic weather, which severely limited the flying windows for bomber aircraft; the massive overstretch experienced by the Wehrmacht and Luftwaffe in its operations in the USSR; and, let it be said, the tenacious defence of their territory by Soviet forces. In arctic climes in 1941 the Germans made none of the gains made elsewhere that year, and despite desperate attempts, were never able to prise Allied control from the port.
Answered by: Robert Lyman, military historian