7 . 5 cm L / 45 M / 16 anti aircraft gun The 7 . 5 cm L / 45 M / 16 anti - aircraft gun was designed and manufactured in Norway in the early to mid - 1920s . It was an uninspired design , but it did boost the anti - aircraft capacity in Norway significantly when adopted . Background and design . Early in World War I , the Norwegian Army realised that aircraft were a threat that needed to be countered . At first , attempts were made to mount existing field gun s on new mounts to allow high angle fire , but it was soon obvious that a more specialised weapon was needed . Attempts were made to buy British and French guns , but both nations needed the weapons themselves because of the ongoing war . The history of the M / 16 can be traced to a letter from the Norwegian Ministry of Defence dated 17 December 1915 . After initial design work had been carried out , it was decided to manufacture one prototype and 12 production weapons . The detailed design work took longer than anticipated , and with the end of the war , any urgency seemed to leave the project . As a result , the prototype was not ready for test firing until 20 May 1920 . The M / 16 was a relatively simple design . It was intended for static emplacement , and was mounted on a pedestal , allowing for 360° sideways movement . The mount allowed for an angle of elevation of between - 1° and 75° . The gun barrel was 45 calibre s long , and had 28 grooves ( rifling ) twisting to the right . The breech block was a semi - automatic horizontal wedge - the gunner had to manually open it to remove the case from the previous shot , but it closed automatically on the insertion of a new round . There was a hydro - pneumatic recoil cylinder under the barrel , with a heavy spring to aid the forward motion of the gun at high elevation . It was originally designed to fire under local command , but was later equipped to receive gun - laying information from a central sight . The gun was also equipped with a device for automatically adjusting the time fuses on the shells . The M / 16 was served by a crew of nine : The gun commander , one soldier for sideways adjustment , one for adjusting the elevation , one to operate the breech block and fire , one loader , one ' fuse adjusting device operator ' , one ' fuse adjuster ' and two to fetch ammunition and take away the empty cases . Service history and fate . A total of 12 production guns were built . Further production was curtailed because of the perceived low risk of war in the 1920s ; by the time the need for more anti - aircraft artillery was obvious in the 1930s , the design was outdated . The M / 16 was employed in the static defence of the various military installation s in Norway . The weapons were moved around as priorities shifted , but at the time the Germans invaded Norway on 9 April 1940 , six guns were mounted near Bergen , four were mounted at the Naval base in Horten ; the remaining two were near Oslo along with more modern weapons , such as the 7 . 5 cm L / 45 M / 32 , to defend the capital . The guns at Horten could have taken part in the battle that occurred in the harbour between Norwegian and German ships ( see the article on HNoMS " Olav Tryggvason " for details ) , but due to unclear lines of command and the unprepared state of the crew , the guns were captured before any shots could be fired in anger . In Bergen , the M / 16 was used to try to shoot down German bombers attacking military targets , but the aircraft flew too low for the guns to be of much use . After the main fortification in Bergen surrendered to the Germans , the anti - aircraft batteries were ordered to stand down . In Oslo , the two M / 16s were mounted in a battery at Gressholmen - a small island in the harbour - and were ideally placed to take part in the battle for Fornebu . Norwegian sources claim this battery shot down one or two German bombers , despite the fact that the crew was untrained ( 17 out of the 44 men had been in uniform for only six days ) and several became shell - shocked or deserted their posts . In addition to this and other problems , one of the guns jammed early - on in the engagement . The fate of the M / 16s after the Germans captured them is unknown , but it is likely they were used to further the Axis cause in Norway during the war .