IJN Battleship Pagoda Masts

The Imperial Japanese navy conducted a more thorough battleship reconstruction programme than any fleet except the Italian, extending ships’ hulls, adding considerable power, and modernising fire control (with added gun elevation to match). The two Fuso-class battleships (Yamashiro is shown) were the first, and their ‘pagoda’ foremasts were the most extreme the Japanese fitted. Note that the ‘pagoda’ was built around the ship’s original tripod foremast. In the 1920s these ships added numerous platforms to their masts, but the ‘pagoda’ represented an attempt to integrate them properly. The complexity of the mast could be attributed in part to the insistence not to combine functions. Thus the Japanese continued to use separate directors and rangefinders, as in World War I British practice. They benefited less than they should have from having multiple directors because their fire-control switchboards and data transmitters did not permit quick switching from one director to another. Note the sokutekiban level, with its separate instrument and range-rate panel. Note too the separation between the battle bridge and the navigating bridge (or compass platform, in British parlance). The device marked ‘Kosherochi Type 91’ is Kosha Sochi Type 91, a high-angle director introduced in 1931. Like the contemporary US Mk 19 (but unlike contemporary British AA directors) it did not incorporate a rangefinder (note the separate 4.5m (14.7ft) rangefinder on this level). The penalty, which was deadly in wartime, was that the rangefinder was not always focused on the same target as the director. The presence of the 3.5m (11.5ft) navigational rangefinder suggests that the Imperial Japanese navy had learned to use plots to maintain the situational awareness needed to execute the complicated tactics it espoused. This drawing was adapted from one in the fire-control report of the US Naval Technical Mission to Japan.

Fuso Class Pagoda Masts

The pagoda structures on the Fuso and Yamashiro were a logical solution to a problem: The superstructure needed to be enlarged, but the small ‘footprint’ had to be maintained. Had the superstructure grown side to side or front to back, it would have interfered with the firing arc of the amidships gun turret.

On Fuso, the pagoda contained the following levels:

-Forecastle deck level (standby room, radio-telephone room, battery room, freshwater tank, toilets)

-Shelter deck level (radio room, telephone control room, stock room, derricks for 9-meter cutters, 12.7cm gun mount, 9-meter cutters, locker)

-Lower bridge deck level (sea-water tank, freshwater tank, 20-meter derrick, storeroom)

-Conning tower platform (conning tower, main gun spare control room, commander’s standby room, captain’s standby room, chart store, and chart room)

-Upper bridge deck (communication command room, electrical room, 3.5-meter rangefinder post, quad 13.2mm AA gun, starboard secondary fire control, port secondary fire control room, secondary gun director, 12cm lookout directors panel, wash-deck locker, 30cm spotlight)

-Compass bridge level (main compass, gyromagnetic compass, chart table, greeting module, transmission room, telegraph room, standby room)

-Lower lookout platform/anti-aircraft fire-control/signaling platform (lookout cabin with 2 telescopes, 7.7mm machine gun, 60cm searchlights, operation room, storeroom, high-angle AA fire director, 4.5-meter rangefinder, protected lookout post, binoculars store, signal flag locker)

-Forward searchlight platform (1.5-meter navigation rangefinder, 60 cm searchlight, 110 cm searchlight, telephone room, vertical deflection measuring stand, quad 13.2 cm AA gun)

-Battle bridge (towing light, double magnetic compass, chart table, signal lamps, compass)

-Upper lookout platform for secondary gun (towing light, secondary gun director, 3.5-meter rangefinder, 12 cm lookout panel, wire room, protected lookout post)

-Lookout and searchlight control level (searching and self-position room, 8cm binoculars, searchlight control panel, awning stanchions, daylight signal lantern, ladder stand, lookout platforms)

-Sokuteki Ban platform (gun control computer, target direction computer, 12cm binoculars, target course and speed measuring stand, standby room, signal lamp, 30cm deck lamp)

-Fire command platform level (15cm spotting stand, radio equipment box)

-Main gun fire command level (main gun director tower, aerials)

-Main rangefinder level (8-meter rangefinder)

Yamashiro had a few other goodies, like control positions for the aircraft catapult on top of the turret. This made her pagoda a little taller.

As for the stability thing, the Japanese insisted that no instability was caused at all. The fact that Fuso blew in half but did not capsize is good evidence to support this claim.

The four Kongo-class battlecruisers, rebuilt as fast battleships in the 1930s, proved to be the most useful Japanese heavy-gun capital ships. Because they were not considered as valuable as the true battleships with heavier main batteries and armour, and because they were so fast (having been re-engined), they were used to screen carriers at Pearl Harbor and for bombardment sorties at Guadalcanal – where two were lost. As in the other rebuilt Japanese capital ships, the ‘pagoda’ mast was built around the original tripod foremast, with additional stiffening for the big rangefinder atop the mast. Note also the characteristically Japanese separation of battle bridge and navigation bridge (equivalent to a British compass platform), with a lookout control deck in between. The big 4.5m (14.7ft) rangefinder on the foredeck was presumably mainly to support tactical plotting, and the lookout control deck may have been a way of coordinating the numerous large binoculars and other optical sensors scattered around the mast. The Hoibans are Scott-type directors. The course and speed measurement device (sokutekiban) was uniquely Japanese, although it seems to have embodied Barr & Stroud-developed technology. Note the separation between the anti-aircraft director (in the enclosure on the AA control deck) and the 4.5m (14.7ft) AA rangefinder just behind it. This drawing was adapted from one in the fire-control report of the US Naval Technical Mission to Japan.

When Nagato was rebuilt, her new ‘pagoda’, shown here, was built around her heptapod mast. As in the ship’s original configuration, the main rangefinder was mounted on tracks, so that it could be moved around the legs of the mast to point in any direction. Note the multiple Type 94 directors (Hoiban; one is marked ‘main director’, but presumably the guns were normally controlled by the mast-top unit). The ship’s anti-aircraft director, using the 4.5m (14.7ft) rangefinder, is not shown. This drawing was adapted from one in the fire-control report of the US Naval Technical Mission to Japan.

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