"Special" Common was family of projectiles designed to replace the older "Common" shells which were seen as obsolete and no longer manufactured. This "Special Common" designation was only a "semi-official" term as it was not always used in official documents, though it was in some, such as OP 1664. This was given to the newer, mostly post-1930, base-impact-fuzed (BDF) Common shells intended for use against surface targets -- as opposed to nose-time-fuzed "AA Common" with no windscreen (confusing!) shells -- with windscreens introduced to get longer range. Initially, the windscreen changes were simply to cut a narrow set of threads into the nose of an existing, older base-fuzed generic Common design (usually with newer fuzes and other updates to create a new Mark Number shell) and screwed on the new windscreen just like had been done by the larger-gun AP shells since early in WWI.

This turned out to be a mistake since, unlike the sacrificial AP cap of the bigger shells, the nose of a cap-less Common (or even such an AP shell if the Navy had decided, like the US Army and British Army/Navy, that capped "AP" shells, which were all such Navy shells, should be called "APC" shells, which the Navy did not do) was NOT "sacrificial" but needed to be intact to penetrate armor (thinner, usually homogeneous armor in the case of base-fuzed Common shells, but armor none-the-less). Cutting "break on the dotted-line" grooves into the nose of such anti-armor shells was an invitation to shell nose breakage on impact, which frequently occurred, especially at any kind of significant oblique angle. Not good.

As such, the US Navy and British and German Navies, decided to add a thin, AP-cap-like nose covering soldered to the nose and cut threads in it at its thickened base-ring, for the windscreen to be attached to. Hence in the US the term "Special" was added, though eventually all but the few oldest Common shells still in service were made such. The US Navy did not want to call this a "cap", since it was not there to act like one on an AP shell, so they came up with a new term, "Hood". Now, there were a few such shells used by the US and Britain and Germany that actually thickened the "Hood" (or whatever it was called in those countries) into a true, though usually thinner, AP cap for a few shells 8" or larger, though most remained just that thin Hood. Most, though, were just regular anti-medium-thickness-homogeneous-armor base-fuzed Common shells with the new, long-point windscreens attached for long range.

During the late-1930s and early in WWII, the many older 6" guns still in service in the US Navy -- submarine deck guns for example -- that were not on light cruisers were seen to have a greater chance of being in fights with what turned out to be German, Italian, or Japanese cruiser warships, including armored conning towers on some submarines, that might require a stronger shell. The 6" Mark 27 and later Mark 33 Special Common shells, though with just the regular thin Hoods, were beefed up until they would have been called true APHE in the US Army, capable of doing anything to a homogeneous-armored ship that the capped AP shell of larger guns could do to face-hardened armored ships; they even had their explosive charge reduced to only about 2.5% like most British and US Army AP/APC shells of the time.

The thicker Hoods made into actual AP caps were used in the US 8" Mark 15 Special Common shell of 1930 (quickly replaced by the "standard" 8" Mark 17 Special Common with a regular thin Hood but greatly strengthened body like the above 6" Common shells a year or so later -- I do not know what ships ever got the Mark 15 Special Common, if any); the British 8" Mark IB SAPC shell (that gun's "APC" shell), and the German 38cm Spgr.m.Bdz. (u.K.) L/4,1 for the BISMARCK guns only.

Thus, the US Navy had "regular" base-fuzed Special Common in its under-6" guns, a quasi-AP-type Special Common in some of its later 6" non-cruiser guns and pre-WWII 8" cruiser guns; and, for a short time around 1930, a true capped Special Common for 8" cruiser guns (may have been available later, if desired, I assume, though by then true AP shells were available for all 8" guns).

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08 June 2021 - New essay