What a the choice of Secondary gun calibre tells us: A UAD infused discussion (Long Patrol)

Four-inch guns could fire rapidly enough to stop small, fast torpedo craft. Larger secondaries made sense once navies expected heavier destroyers or cruisers and accepted the extra weight and complexity.

A mixed 15-inch, 6-inch, and triple 4-inch battery illustrates how intended opponents shape a battlecruiser's armament.

Once dreadnought main guns could handle armoured opponents, secondary batteries focused on destroyers and torpedo boats.

Triple four-inch mounts sacrifice shell weight for more chances to hit fast, manoeuvring torpedo craft.

Six-inch secondary guns signal an expectation of cruiser threats while the main battery engages capital ships.

Troubridge's ruined career after a prudent decision helps explain why Arbuthnot chose visible aggression at Jutland.

Destroyers receive priority because an overlooked torpedo attack can be more dangerous than cruisers the faster battlecruisers can outpace.

Secondary calibre and mount layout offer clues to the enemy force and attack patterns a navy expected to confront.

Single or multi-barrel mounts suggest different attack patterns, while larger destroyers make six-inch fire increasingly attractive.

A battleship can omit some defensive guns only when escorts and the main battery can reliably defeat the threats those weapons cover.

Ships expected to operate alone need weapons for more kinds of threat, helping explain the complex batteries of Bismarck and Tirpitz.

G3's planned 16-inch, six-inch, 4.7-inch, two-pounder, and torpedo weapons each answer a different layer of threat.

The G3's speed, range, and six-inch guns point beyond a North Sea battle line toward distant commerce-war roles.

Gun types and quantities preserve evidence of intended missions that surviving documents may not state plainly.