Don't underestimate the power of the Big Seven. - Nagato
Nagato class' 2nd ship and from there, Mutsu. Of course, I'm part of the world's big 7. - Mutsu
Big Seven, sounds quite fancy eh. Yep, like most of us know, Big 7 are title for Battleships during World War 2 that was armed with 406mm (41cm actual value) or 16 inch Cannnons. Like the title implies, Big Seven, only owned by 7 Warships in the world during World War 2. The holders are HIJMS Nagato, HIJMS Mutsu, HMS Nelson, HMS Rodney, USS Colorado, USS Mary Land and USS West Virginia.
"B-but, Iowa-class and some other Big Battleships also have same 41cm cannon or larger. Why they don't have Big 7 Title too?" Well, this also has been bugging me until I do some research around and I found why. This might end up as wall of text but I'll try to keep it simple.
Origins of Big 7 Title[]
Like the statement above, Big 7 was only for Battleships that armed with 41cm cannons. But that's not all. Nagato, Mutsu, Nelson, Rodney Colorady, Mary Land and West Virginia are all built before the Washington Naval Treaty started. Based on the Treaty :-
- Capital ships (battleships and battlecruisers) were limited to 35,000 tons standard displacement and guns of no larger than 16-inch (406mm/41cm) calibre.
That is part of reason why Battleships that was built after the treaty are not part of Big 7. All ships/cruisers that was built after the Treaty are armed with a bit smaller calibre guns to respect the Treaty agreement. Japan however announced their denunciation on Washington Naval Treaty at December 29, 1934. Japanese ignored the treaty after they sent the formal notice to terminate the treaty until 1936, 3 years before World War 2 started,
Conclusion
Big Seven title was only given to first 7 of Battleships that was armed with 41cm (16 inch) cannon before Washington Naval Treaty started and with Japanese ending the treaty, right before World War 2 started. The treaty ends and bigger ships like Iowa-class and Yamato-class are built after/during the treaty, ignoring the Naval Arms limitation.