As you likely know, the standard large coast artillery in Dutch service in the NEI consisted mainly of various models of Krupp and Bofors 150mm guns. Late acquisition, however, included fewer than a dozen Bethlehem Steel 7-inch (178mm, more commonly expressed as 180mm) guns originally installed in two late classes of American predreadnoughts. These broadside guns were emplaced on pedestal mounts in hull casemates, as seen in USS Vermont
sometime during the early 20th century (she has her original livery and masts).
Because these guns when made were designated in the English common system, I’ll provide that datum first, and the metric equivalent in parentheses.
The USN Mark II (later Mark 2) 7-inch/45caliber BLR weighed 12.8 short tons (13 tonnes) and although considered marginally a rapid-fire weapon, could deliver only four rounds/minute. Little wonder, as its projectiles weighed 165 pounds (74.8 kg). Lying between the true RF maximum of the 6-inch (152mm) gun and the true BLR of 8-inch (203mm) bore, the 7-inch gun was neither fish nor fowl, and quickly disappeared in the subsequent dreadnought generation. There were, however, substantial numbers of these guns placed into storage, and such pieces saw WWII service in both American and Dutch hands.
The projectile length, in various marks, varied from 23.64 to 23.73 inches (60.1 to 60.3 cm); the propellant was normally 58 pounds (26.3 kg) of SPD, achieving a reasonably good 2700 ft/sec (823 m/sec) of muzzle velocity (much higher, and severe bore erosion began to occur, much shortening barrel life). On its original pedestal mount, with a maximum elevation of 15°, typical for the time, the gun reached 16,500 yards (15,090 m) as an effective range. By any standard, however, a 7-inch gun was a powerful weapon, and restricting its maximum effective range to 15 km meant a real waste. So, what to do about it? That remains a thorny question.
The Dutch in the NEI didn’t have much time and they knew it. Not only that, but much/most of the American export ordnance matériel arrived late in the game, shortening the available installation time even more. Most of the eleven Bethlehem 7-inch guns the Japanese captured when they arrived in Java were not installed; two at Ceribon were partially so; three on Madoera Island were completely or almost completely done. From evidence seen in other former Dutch colonies, for example in Suriname, ex-American naval guns are installed on their original pedestal mounts, implying that any battle (against raiders or U-boats) would be at relatively short range. The Dutch last-ditch fortress on Madoera may have involved modified mountings, permitting these ex-Yankee 7-inch (180mm) naval guns greater elevation and range. I am merely suggesting this, and do NOT know it for a fact. Nuyt may know.
Stored 7-inch naval guns saw brief WWII service in emergency coast artillery batteries on the American coasts, emplaced as was until better and longer-range batteries could be built; such guns saw longer service in the hands of the Marine Defense Battalions on several Pacific islands.