was thick. Engineering The engineering plant included 16 coal-fired Babcock & Wilcox boilers (32 Niclausse boilers in the Cramp-built Pennsylvania and Colorado) supplying steam to two inverted vertical four-cylinder triple-expansion engines, totaling for as designed. On trials South Dakota achieved at . The normal coal allowance was 900 tons, but this could be increased to 2,000 tons. Refits In 1909–1911 the ships' original 8-inch/40 caliber guns were replaced with four /45 caliber Mark 6 guns in Mark 12 turrets due to a gun bursting on Colorado in 1907. From 1911 the military foremasts were replaced with cage masts. In 1911, Pennsylvania was fitted with an after flight deck for the first landing on a ship by an aircraft. This was a one-off demonstration on 18 January 1911 with pilot Eugene Ely, who had performed the first takeoff from a ship on two months earlier. From 1915 to the American entry into World War I in April 1917, Huntington and two Tennessee-class ships had catapults for seaplanes (which disabled the after turret) and carried up to four aircraft; Huntington could also tether an observation balloon, which was used during convoy escort duty in the war. However, by late 1917, the aircraft program was cancelled and the catapults removed. During the US participation in World War I several changes were made to these ships. All but four of the 6-inch guns were removed to arm merchant ships and reduce the potential of flooding through the lower casemates; this was a factor in the loss of San Diego (probably to a mine) in July 1918. The 3-inch single-purpose guns were reduced to ten, while two 3-inch/50 caliber anti-aircraft guns were added. However, the official Ships' Data Book series indicates that by 1921 all of the 6-inch guns were remounted, only to be dismounted again by 1929. By 1919 the 32 Niclausse boilers in Pittsburgh (ex-Pennsylvania) and Pueblo (ex-Colorado) were replaced by 20 Babcock & Wilcox boilers. By 1921, Pueblo had 16 Babcock & Wilcox boilers, while Pittsburgh had 12 Babcock & Wilcox and eight "modified Niclausse" boilers. In 1922, Pittsburghs forward funnel and the associated boilers were removed, leaving her with 12 Babcock & Wilcox boilers. In 1922–1923 modernization of the eight survivors of these ships and the Tennessee class was considered but not implemented. Possible upgrades would be new boilers and engines for a speed of , a more seaworthy bow, protection