QF 2磅Mark II本質上是維克斯生產的QF 1磅馬克沁炮的放大型版本。這是一門40毫米口徑的火炮，裝有水冷式炮管和維克斯—馬克沁機構。1915年，英國皇家海軍訂購了它，並且用作巡洋舰尺寸及以下船隻的防空武器。最初的型號是以手動裝填的14發布製彈鏈所供彈，其後由彈數相同的钢製彈鏈所取代。這種“按比例放大”的過程並不完全成功，因為它導致機械裝置變得相當輕便，而且容易產生故障，例如彈藥從彈鏈以上掉下來。1915年，16門2磅炮搭載在裝甲貨車以上，以用作皮爾斯箭式裝甲防空貨車（英语：Pierce-Arrow armoured AA lorry）的主武器。1918年，其中一門火炮獲實驗性地架設在英國陛下之飛艇23r（英语：23-class_airship）的上隔間以上。[5]
第二次世界大战當中，倖存的武器被搬出倉庫並再度服役，主要用作軍用拖網船（英语：Naval trawler）、摩托艇和“武裝遊艇”等船隻所載武裝。它幾乎僅用於單管無動力炮架P Mark II（英國皇家海軍的命名法會賦予炮架和火炮各自不同的Mark編號），而只有少量武器用於Mark XV炮架，為雙管動力型炮架裝備。由於它們太重，無法在海上使用，因此被安裝在沿岸上。1944年全部報廢。
Mark VIII（手動型）和Mark XVI（電動型）單管式炮架亦得到了廣泛使用，主要用於小型護航艦艇（比如“花”級护卫舰）和沿海船艇（尤其是早期的Fairmile-D（英语：Fairmile D motor torpedo boat）機動炮艇（英语：Motor Gun Boat）型）。Mark XVI的炮架與厄利孔20毫米机炮的雙聯炮架Mark V和波佛斯40公釐高射砲的“博凡”式（Boffin）炮架有關。一個有趣的功能是容量非常大的彈匣，從八聯裝炮架的每門火炮140發到單管式炮架的56發。[10]如此龐大的彈藥容量使得八聯裝炮架直到需要重新裝彈以前能夠連續射擊73秒。由於倍徑長度相對較小（L/39），因此初速僅達到了2,040英尺／秒（622公尺／秒），隨之而來的是最大射程僅約3,500公尺。為了解決這個問題，就在第二次世界大戰爆發以前的1938年，為砰砰炮而研發了重達1.8磅（820克）的高速（HV）彈藥，增加了推進劑的裝藥量，將新的炮口速度從2,040英尺／秒提高至2,400英尺／秒（732公尺／秒）。
英國皇家海軍認為，砰砰炮對付魚雷機時，多座砰砰炮的成效大約僅僅是每門波佛斯炮的一半；但對付特別攻擊隊隊員時卻大致相等。[21]到第二次世界大戰結束為止，在英聯邦海軍當中，砰砰炮是一款無艦不在的武器，其數量超過了波佛斯炮，並且擊落了眾多軸心國的飛機。[22]在其後的創新，例如將遙控電源控制（英语：Glossary_of_British_ordnance_terms#RPC）（Remote Power Control）與配備雷達的測速儀（速度預測）指揮儀相結合，極大地提高了準確度，而且還解決了引信和可靠性等方面的問題。而由於20毫米口徑厄利孔機炮的制止力並不足以抵抗日本的神風特攻隊飛機攻勢，加上波佛斯炮的數量也不足以滿足需求，因此在戰爭結束以前，這款單管式裝置獲准延期服役。
^Patrick Abbott and Nick Walmsley, British Airships in Pictures: An Illustrated History, House of Lochar 1998, ISBN1-899863-48-6 (p.62)
^ 6.06.16.26.36.4I.V. Hogg & L.F. Thurston, British Artillery Weapons & Ammunition 1914-1918. London: Ian Allan, 1972, Page 28.
^Bagnasco, Erminio. Le armi delle navi italiane. Parma: Albertelli. 1978: 77–80. ISBN 978-8887372403.
^Raven and Roberts, British Cruisers of WW2, p224. “第一台八聯裝炮架重達11.8噸，而遙控電源控制架和1.6噸（共1,200發）彈藥則重達17.35噸。”（The first eight-barrelled mounting weighed 11.8 tons while a Remote Power Control mount along with 1.6 tons (1200 rounds) of ammunition weighed 17.35 tons.）
^Campbell, Naval Weapons of WW2, p67 and p149. “坎貝爾指出，四聯裝美國海軍波佛斯炮架重達11.12至11.88噸，炮架以上每門火炮最多只能裝填10發炮彈。”Campbell notes that a quad USN Bofors mount weighed 11.12 to 11.88 tons and only carried a maximum of 10 rounds per gun on the mount.
^原文：Among the machine guns under consideration were the Army's 37-mm and the British Navy's 2-pounder, more commonly known as the "pompom." The decision soon narrowed to a choice between the Bofors and the British gun. The British were anxious to have their gun adopted, and the fact that British aid would be readily available in initiating manufacture was put forward as an argument in favor of its selection. The 2-pounder, moreover was giving a good account of itself on British ships. On the other hand, there was the distinct disadvantage that the gun was designed for cordite powder, and no manufacturing facilities for the production of this ammunition were available in the United States. Thorough study revealed that the gun could not be converted to take American powder. Another consideration was muzzle velocity: The pompom had a relatively low velocity, 2350 feet per second as compared with 2830 for the Bofors. The success of the pompom in action was more than offset by the proved qualities of the Bofors in the hands of a number of powers who were using it, and the Bureau decided to join that group. Shortly after the Bureau's selection of the Bofors, British naval officials also decided to adopt the gun.
^Rowland and Boyd, U. S. NAVY BUREAU OF ORDNANCE IN WORLD WAR II, USN Bureau of Ordnance, p223-224.
^Middlebrook, Battleship, p. 340. “該報告並無提到被威爾斯親王號所搭載的40毫米波佛斯炮擊殺、甚至沒有波佛斯炮命中的內容，而砰砰炮火力下的命中卻是由當時威爾斯親王號的艦員所記錄了。”（The report does not note any 40mm Bofors kills or even hits from the Prince of Wales' Bofors gun, while hits from pom-pom fire were recorded by the crew of the Prince of Wales.）
^Middlebrook, Battleship, p. 340: “據認為，一門由駐台所控制並且發射曳光彈的波佛斯炮是一款要比由指揮儀所控制但無曳光彈的八聯裝砰砰炮更有價值的武器…”（"It is considered that a Bofors with tracer ammunition in local control is a more valuable weapon than an 8 barrelled pom-pom in director control without tracer..."）
^Brown, A radar history of World War II: technical and military imperatives, p. 220. “布朗指出，當威爾士親王號從新加坡出發時，四台282式雷達當中有三台停止工作。”（Brown notes that 3 out of 4 type 282 radars were out of service when Prince of Wales departed Singapore.）
^Garzke and Dulin, Allied Battleships, p. 204, “請注意，在第一次遭受魚雷打擊以後，剩餘的282式和兩台285式搜索雷達失效。”（notes that the remaining type 282 and two type 285 radars failed after the first torpedo hit.）
^Campbell, Naval Weapons of WW2, p. 67: “…如果控制和炮架裝置的效率相同，波佛斯炮對付魚雷機的成果被認為是砰砰炮的兩倍，但對像神風特攻隊這樣的近距離目標卻沒有那麼好。”（"...if control and mountings were of equal efficiency, the Bofors was reckoned to be twice as effective as the pom-pom against torpedo planes but not much better against very close range targets such as Kamikazes."）
Louis Brown, A radar history of World War II: technical and military imperatives. Institute of Physics Publishing, 1999. ISBN0-7503-0659-9.
John Campbell, Naval Weapons of World War Two. Naval Institute Press, 1986. ISBN978-0-87021-459-2.
Rowland and Boyd, U. S. NAVY BUREAU OF ORDNANCE IN WORLD WAR II, USN Bureau of Ordnance
Garzke and Dulin, Battleships: Allied Battleships of World War II. Naval Institute Press, 1980. ISBN978-0-87021-100-3.
I.V. Hogg & L.F. Thurston, British Artillery Weapons & Ammunition 1914-1918. London: Ian Allan, 1972
Martin Middlebrook and Patrick Mahoney, Battleship: The Loss of the Prince of Wales and the Repulse. Penguin Classic Military History, 2001. ISBN978-0-14-139119-9.
Alan Raven and John Roberts, British Cruisers of World War Two. Naval Institute Press, 1980. ISBN978-0-87021-922-1.
