The Pacific War Online Encyclopedia
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Copyright 2004 Project Liberty Ship
|Tonnage||3478 light displacement tons
10,419 deadweight tons
|Dimensions||441'7" by 56'11" by 27'6"
134.59m by 17.35m by 8.38m
|Maximum speed||11 knots|
||Plastic armor splinter protection to portions of superstructure
reciprocating engines (2500 shp)
Two water-tube boilers
|Bunkerage||1700 tons fuel oil|
|Range||17,000 nautical miles (31,000 km) at 11 knots|
The Liberty Ships (officially Maritime Commission standard EC2-S-C1 emergency cargo ships) were one of the great production triumphs of the Allies in the Second World War. These ships were built as quickly and cheaply as possible, with a "programmed obsolescence" of just five years, with the first ship (the Patrick Henry) being launched in September 1941. The idea was that they could be produced faster than the U-Boats in the Atlantic could sink them. One shipyard set a record of laying down and launching a Liberty Ship in just 24 hours. This was not typical, of course, but many yards were routinely launching Liberty Ships a month after laying them down, and Oregon Shipbuilding sustained a production rate of 17 days on the ways through the middle of 1943.
Heavy British shipping losses in the winter of 1940-41 prompted the British to press the U.S. Maritime Commission to to mass produce 11-knot, 10,000-ton cargo ships. The design was based on British Ocean-class cargo ships ordered from American yards in 1940, modified to burn oil rather than coal and use water-tube instead of Scotch fire-tube boilers. The hull form was modified for easier construction and the crew's quarters were placed in a single amidships deck house resembling those of Maritime Commission standard types. Masts were used instead of king posts. The use of an old but reliable triple-expansion reciprocating engine design helped ensure that the machinery could be manned by inexperienced crews while avoiding a competition with warship construction for more modern geared turbine machinery. Welding was used extensively in their construction, though most Liberty Ships had the frame riveted to the shell. Wood was avoided in their construction, except that wooden hatch covers were used, which doubled as rafts if the ship was sunk. Oddly, 0.25" steel and plastic armor (made of asphalt and crushed stone and up to 6" thick) was provided for critical areas of the superstructure. The resulting ships fell far short of the quality of the standard (C1, C2, and C3) cargo ships, but were regarded as a necessary evil.
The ships had five cargo holds, with capacities of 76,077; 134,638; 83,697; 82,263; and 82,435 cubic feet (2154, 3813, 2370, 2330, and 2334 m3). There were also three deep tanks, for dry storage or ballast, with a combined capacity of 41,135 cubic feet or 1165 m3.The ships were originally designed with five-ton booms only. The need to load tanks and other heavy equipment let to the installation of 15-, 30-, and 50-ton booms.
Liberty Ships originally cost about $1,750,000 apiece and were expected to take about five months to complete. The cost varied from yard to yard due to the use of different kinds of contracts, including "price-minus" contracts (a more politically acceptable variation of "cost-plus" contracts). Incentives were built in to the construction fees to encourage efficiency. The fees themselves were initially as much as 10% of the costs of the ships, but were steadily negotiated down during the course of the war, to as little as 1% in some cases. It was expected that the yard would initially produce about two ships per way per year, increasing to four ships per way per year as the yards gained experience. In fact, completion time averaged about 250 days in 1940 but dropped to an average of about 45 days by 1944, of which just 30 was spent on the ways. A construction time of about 250 days for the first ships from a yard, dropping to around 50 days within six months, was a remarkably consistent feature across yards no matter where or when they began operations.
Standardization was the key to rapid manufacture of Liberty
Ships. When plans called for the manufacture of a thousand ships with a
thousand identical rudders and sternposts, the steel manufacturers could
afford to set up special equipment for fabrication. This allowed
Bethlehem Steel Co., for example, to turn out rudders at the rate of 120
per month. Similar economies of scale were present in machinery and
boiler manufacture, even when engine manufacture was spread across
14 companies and boiler manufacture across 11 (though Babcock and
Wilcox and Combustion Engineering Co. produced the lion's share of
boilers.) Multiple suppliers supplying parts to multiple shipyards meant that there was a steadier flow from suppliers to yards.
The original Liberty Ship design called for 75 different thicknesses of
steel plate; when steel plate production fell behind demand, the plans
were revised to require only 27 different thicknesses of steel plate.
The name "Liberty Ship" was a propaganda invention that took
some time to work up. In his 3 January 1941 announcement of the
emergency shipbuilding program, Roosevelt referred to
the design as a "dreadful looking object", and Time described the ships as "Ugly
Ducklings." By May 1941 the Maritime Commission saw the need for a more
positive label, and asked that the ships be consistently referred to as
"Emergency Ships." It was suggested at the same time that those
operating under the American flag be called the "Liberty Fleet."
However, in the wake of the widely publicized launching of Patrick Henry, the term "Liberty
Ship" came into widespread use.
A total of 2708 Liberty Ships were
constructed during the war, with a total deadweight
tonnage of 29,182,000 tons. This was about 46% of all hulls and 42% of
total deadweight tonnage constructed under the Maritime Commission
program. Production ramped up from just 2 ships in
December 1941 to a peak of 128 ships in November 1943, then ramped back
down to less than ten ships a month in late 1945.
These ships were not without their disadvantages. They had definite structural weaknesses, and their welded construction was sometimes unreliable. A few ships broke apart in the heavy seas of the North Atlantic where cold temperatures made the steel plating brittle. The ships were judged too slow at 11 knots to be economical in a peacetime economy. Nevertheless, and in spite of their "emergency" nature, many Liberty ships were still plying the waves thirty years later.
The production schedule below is total production.
The number actually allocated to the Pacific is less easily
ascertained, but theoretically should have been roughly 30% of the
total except in the first and final months of the Pacific War.
Geoghegan (2001; accessed 2012-7-19)
Project Liberty Ship (accessed 2007-1-1)
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