Craig here.

Brad gave a good description of the terminology used with the “big guns.”  In my studies of the Civil War, gun breeches were typically closed since most of those fine cannon were muzzle loaders.  A few, definitely the minority, were breechloaders, pointing to the future.  Forty years later, at the start of the 20th century, all guns in the US Army and Navy, save a few ancient Civil War types retained in reserve, were breechloaders.   The evolution of breechloading was as important to the overall gun system as rifling and recoil systems.

To help visualize the difference between interrupted screw and sliding breech-blocks, let me pull up some photos from the USS Olympia, with guns dating to the 1890s.  Here’s a the breech block from a 5-inch gun:

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Notice the breech block (to the right).  It has two “steps” of threads.  Notice also the locking lug in the center of the step closest to the camera. The tube running from under the gun to the 11 o’clock position is, I think, part of the exhaust venting system.  If  I’m correct that tube blasted compressed air into the breech after firing to force the fumes out the muzzle end.

Closer look at the block:

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So there’s a flat step, an intermediate threaded step, and a top threaded step.  There’s also an obturation cone at the front face of the block (left side in this view).  That cone pressed against the gun where the chamber met the breech, sealing off the escape of gas when the gun was fired.  Again notice the locking lug.  The threads and lug matched into the breech end of the gun:

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Again a flat, intermediate and top step, with the last two threaded.  There is a “seat” for the obduration cone in the mouth of the breech.  Also notice the trail for the locking lug at the upper left.  A trace shows the path of the locking lug as the block entered and turned within the breech (sorry for the fuzzy photo).

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So the top threaded step with the locking lug entered the breech against a “flat” step, then it turned about 45 degrees to lock against the intermediate step in the breech.   Here’s a view of a similar 5-inch gun with the breech closed.  Notice the entry slots for the steps (from 9 o’clock to about 11 o’clock).  Also notice the open hole in the center for the primer.

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There were of course several variations on the interrupted screw.  This particular block uses the British Welin system, with the steps in the screw.  The French de Bange system lacked the “steps.”   But the principle was generally the same – a slotted breechblock inserted into the breech then turned and wedged in place using threads.

A few steps away is a sliding breech block on one of the Olympia’s 6-pdr guns.

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On this example, the breech block hangs low, reading for loading.  Missing on the side of the breech is a handle that gunners used to push the block up and against the breech face.  Here’s a view from the back.

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This gun used a “U” jaw.  Other sliding block guns had open jaws (without the lower end of the “U”) or closed jaws (with only a hole in the breech to insert the round.  The gunner worked a handle (missing here but the axis of the mechanism sticks out to the left) which in turn worked to draw the block upwards.  The trace of action would press the block against the breech face. Hard to see, but the upward trace of the block is not true perpendicular to the line of the bore. It is instead slightly angled towards the muzzle, thus pressing the block against the breech tightly as the block is driven upwards.

In some weapons a two-action motion would also push a small obduration cone into the mouth of the breech.  But in most systems, a brass case provided sufficient closure to seal the breech against gas leaks.  Here’s a view of another 6-pdr with the block in the closed, or firing position.

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Note the “U” shape of the top of the block.  This cleared the breech block when in the loading position.  But there is a small gap between the top of the breech mouth and the block.

For reference, the 6-pdr is 57mm caliber weapon.  Generally, but certainly not absolutely, sliding blocks are found on guns using fixed ammunition.  Interrupted screws worked better where bagged propellant charges are used.

Save the Olympia!

I’ve mentioned the status of the cruiser USS Olympia a few times on my own blog (here, here, and more recently here), and CDR Salamander discussed it last spring.

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For those unfamiliar, the Olympia is docked in Philadelphia, Pennsylvania (actually opposite the USS New Jersey on the Delaware River), and is the featured exhibit of the Independence Seaport Museum.    However the ship is in bad shape physically, although from the photo above she seems presentable.  The lower internal spaces and external sections below the waterline need maintenance.  The Olympia is over 100 years old, so what do you expect?

The cost?  I’ve seen estimates ranging up from $20 million.

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The back story is that over the last decade, the museum’s maintenance budget shrank, partly due to reduced revenue from tourism.  Some in Philly have argued the lack of focus by the community on the water front is the blame there.  But some of the problem is lamentably a horrible example of corruption.  An opinion piece on the US Naval Institute site last year summed it up well:

As the Olympia sat deprived of basic maintenance, the Independence Seaport Museum’s chief, John S. Carter, enjoyed perks far above compensation provided at peer institutions. In 2004, his salary exceeded $350,000, and he lived rent-free in a $1.7 million executive mansion bought, maintained, remodeled, and even furnished with museum funds, according to news reports.

Carter received a 15-year prison sentence in 2007, removing him from the situation.  But the Olympia remained in peril.  Last year, the Museum announced plans to close the ship for good in November.  Some suggested the ship would eventually become an artificial reef or simply go to the scrapyard.  Those plans remain on hold.  The Olympia remains open, at least until the spring of this year.  I’m told that a board meeting in March will lay out future plans for the ship.

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Currently two groups, outside the museum, have stepped forward to offer preservation options for the ship.  The Friends of the Cruiser Olympia have a long-range plan to acquire the ship and, following refurbishment, continue to display it on the Philadelphia waterfront.  Last month another group, the Mare Island Navy Yard Association, in Vallejo, California proposed returning the Olympia to the place she was built.

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Setting aside the logistical questions about a trip through the Panama Canal, the important component for the ship’s future should be preservation.  The Olympia is a national treasure.  Historian Dr. Benjamin F. Cooling called her “Herald of Empire” and an icon of the American century (you might pick up his book detailing the history of the ship if you are interested in this subject).

She is the last surviving warship of her time.   Admiral George Dewey led the US fleet into Manila Bay from the decks of the Olympia.   Aside from action in the Spanish-American War, the Olympia saw service in World War I (and brought home the remains of the unknown soldier from that war now buried at Arlington).   Her machinery and armament are engineering landmarks of which few similar examples exist today.

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And there is also the story of the sailors who served on board the Olympia.  The ship serves as a three-dimensional artifact for us to connected back to their times.  And don’t get the idea the Olympia’s tale is all bosun’s whistles and cannon blasts.  Photographs of the ship’s complement in her early years show a mixed crew.  A reminder that the navy was un-segregated well before it was segregated, and then later de-segregated.  There’s a story there aching to be told.

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I submit that $20 million is a cheap price to pay in order to preserve such an artifact for later generations.  These days we talk of billion dollar TARP bills.  There are a score of Defense projects who’s comptrollers would consider $20 million a small deviation from baseline projections on their assigned projects.  I think we can afford to spend that amount for the preservation of the USS Olympia.