Jane's Naval Gun Notation

Fred Jane had devised a notation to describe the power of guns, which was intended partly for use in his wargame and partly for use by naval officers and analysts for comparing ship capabilities. The notation used in 1903 used capital letters, sometimes with numbers appended:

Notation   Gun      Length  Muzzle Velocity   Projectile Weight

A5         16.25in  30      2,087 ft/sec      1,800 lbs
A3         13.5in   30      2,016 ft/sec      1,250 lbs
A4         12in     40      2,750 ft/sec        850 lbs
A3         12in     35      2,367 ft/sec        850 lbs
B          10in     30      2,040 ft/sec        500 lbs
BA          9.2in   45      2,550 ft/sec        380 lbs
B           9.2in   40      2,347 ft/sec        380 lbs

Jane then rated armour with similar letters, so that you could tell what gun could penetrate what armour at close range. The numbers were altered at longer ranges.