The Norwegian pre-war army had no anti-tank guns, and if needed they had to rely on field and mountain guns used provisionally in this role.*
Despite having no AP-ammunition this measure was actually used with a fair amount of success during the German invasion. At close ranges the thinly armoured Pzkpfw I and II were vunerable to direct fire from field guns, even if they only had HE-ammunition.*
As an example Sargeant Haddeland of Mountain Artillery Battalion Nr.2 destroyed atleast 3 and damaged several more panzers during the campaign in the Valdres Valley in late april 1940 using a 75mm mountain gun.*
On one occasion some old british 76m AA-guns from WW1 were pulled out from storage aswell and used as static AT-guns in defence of a position, albeit unsuccessfully.*
*
