Crushed lightweight (expanded clay) aggregate was utilized in the 120 
pef concrete of 11 of these 12 ships (Boyd, et. al., IAD) 5, ihe ate 
apropos to note that drill cores extracted about 1953 from the hull of 
the wrecked Selma, constructed of this lightweight concrete, revealed 
no corrosion of reinforcing steel after 35 years of exposure to sea- 
water (Mather, 1969). In addition to the 12 concrete ships actually 
built in America during World War I, a total of 32 concrete barges 
(ranging from 500 to 1200 gross tons) were also built; 21 were used on 
the Erie Canal and Hudson River and 11 were used at New York Harbor. 
Most of these barges were too easily damaged by blows that would not 
have been severe enough to impair the serviceability of either wooden 
or steel vessels. Moreover, also constructed at that time were three 
100 foot tankers and five lighters (each 500 gross tons). The greatest 
shortcoming of these various concrete ships and barges was the extreme 
brittleness of the concrete. The record of performance indicated some 
doubts that reinforced concrete ships and barges would ever become 
commercially popular. Despite such negative attitudes, the consensus 
regarding general characteristics disclosed that concrete ships served 
their intended purpose in World War I. In passing, it is of interest 
to note that concrete ship construction is more economical along the 
Pacific coast than elsewhere in the continental U. S. because of 
equable climate. The history of the American concrete ships has been 
described (Haviland, 1962) and summarized previously (Jackson and 
Sutherland, 1969). 
In Great Britain, during 1943 and 1944, the construction of 
enormous concrete floating caissons known as ''Phoenixes" ( a military 
code name) was accomplished as part of the invasion harbors known as 
"Mulberries'' which were installed, after being towed across the English 
Channel, along the coast of Normandy. Mulberry A (the American harbor) 
was located off Omaha Beach; and Mulberry B (the British harbor), off 
Utah Beach. These 146 caissons were constructed as precast concrete 
units which necessitated 330,000 cubic yards of concrete and 31,000 
tons of reinforcing steel, and involved 1,500,000 square yards of 
forms. The labor force approximated 20,000 men (Billig, 1955). The 
units ranged from 176 to 204 feet in length and were as high as 60 
feet (Stanford, 1951). Other published data (Wood, 1948) indicated the 
use of 410,000 cubic yards of concrete for Phoneix units and an additional 
132,000 cubic yards for supplementary caissons. The bridge-carrying pre- 
cast concrete pontoons, known as ''Beetles'", were 50 feet long by 22 
feet wide by 9 feet high (hull proper). For the Phoenix concrete, the 
ageregate/cement ratio was 4.5, maximum size of crushed stone aggregate 
was 3/4 inches and the designed compressive strength was 850 psi. For 
the Beetle concrete, maximum size of aggregate was 3/8 inches and the 
designed compressive strength was 1500 psi. The intended life of these 
units was 90 days. 
Meanwhile, America was constructing ships and barges as part 
of the U. S. Maritime Commission program that was underway in 1942. 
These vessels were built at five concrete shipyards, namely, Savannah, 
