Editing O'Brien-class destroyer (section)

== Design ==
As built, the ''O'Brien''-class ships were {{convert|305|ft|5|in}} in length ([[length overall|overall]]), were {{convert|31|ft|2|in|m}} [[abeam]], and had a standard [[draft (ship)|draft]] of {{convert|9|ft|6|in|m}}.<ref name="Con-122-123"/> The hull shape featured the distinctive high forecastle typical of U.S. destroyer classes since the 1908–09 {{sclass|Smith|destroyer|4}}, the first destroyers designed to be truly ocean-going vessels.<ref name=Con-121>Gardiner, p. 121.</ref> The ships [[displace (ship)|displaced]] between {{convert|1020|and|1090|LT|MT|lk=on}} with a median of {{convert|1050|LT|MT}}.<ref name=Bauer-171 />

The ships were equipped with two [[propeller shaft (ship)|propeller shafts]] and two direct-drive, [[Heinrich Zoelly|Zoelly]] [[steam turbine]]s fed by four [[White-Forster boiler]]s. The power plant of the ships generated {{convert|17000|shp|lk=in}} which drive the ships to the design speed of {{convert|29|knots|lk=in|kph}}.<ref name=Con-123>Gardiner, p. 123.</ref> Because of inherent inefficiency of turbines at low speeds,<ref name=Friedman-25>Friedman, pp. 25, 27.</ref><ref group=Note>While turbines were most efficient at high speeds, [[screw propeller|propellers]] were most efficient at low speeds. Turbines directly connected to the [[propeller shaft]]s—as was the case with the main turbines of all the ''O'Brien'' ships—were particularly inefficient at low speeds. See: Friedman, pp. 25, 27.</ref> all of the ships were equipped with supplemental cruising engines for travel at speeds under {{convert|15|knots|km/h}}.<ref name=Friedman-29 /> All except {{USS|Cushing|DD-55|2}} were equipped with supplemental [[triple-expansion steam engine|triple-expansion]] reciprocating engines: {{USS|O'Brien|DD-51|2}}, {{USS|Nicholson|DD-52|2}}, and {{USS|Winslow|DD-53|2}} each had a pair of reciprocating engines for cruising; {{USS|McDougal|DD-54|2}} and {{USS|Ericsson|DD-56|2}} were outfitted with only one. Instead of reciprocating engines, ''Cushing'' was equipped with a pair of geared steam turbines for cruising.<ref name=Bauer-171 />

The main battery of the ''O'Brien'' class consisted of four {{convert|4|in|mm|adj=on}}/50 Mark 9 guns.<!-- number, size --><ref name=Con-123 /><!-- calibers --><ref group=Note>The ''50'' denotes the length of the gun barrels; in this case, the gun is 50 [[calibers#Caliber as measurement of length|calibers]], meaning that the gun is 50 times as long as it is in diameter, {{convert|200|in|m}} in this case. The Mark number is the version of the gun; in this case, the ninth U.S. Navy design of the 4-inch/50 gun.</ref> They were also equipped with four twin {{convert|21|in|mm|0|adj=on}} torpedo tubes, for a total load of eight [[Mark 8 torpedo]]es. Although the General Board had called for two [[anti-aircraft warfare|anti-aircraft guns]] for the ''O'Brien'' class, they were not originally outfitted with the weapons; the later {{sclass|Sampson|destroyer|4}} was the first American destroyer class so armed.<ref name=Friedman-31 /> Likewise, there is no record of any of the ''O'Brien'' ships being outfitted with mine-laying apparatus. During World War I, most American destroyers were used in [[anti-submarine warfare]] roles, and were equipped with [[depth charge]]s and delivery systems, such as [[Y-gun]]s and depth charge racks.<ref name=Con-121 /> ''O'Brien''-class ships were equipped with depth charges during the war,<ref name=DANFS-all_six /> but no specific mentions of the types of depth charges used or delivery system are recorded in secondary sources.<ref name=Bauer-171 /><ref name=Con-123 />

=== Comparisons with other "thousand tonners" ===
The "thousand tonners" were the 26 United States Navy destroyers of five classes—''Cassin'', ''Aylwin'', ''O'Brien'', {{sclass|Tucker|destroyer|5}}, and ''Sampson''—so named because they were the first U.S. Navy destroyers to have displacements greater than 1,000 long tons<!-- not converted since it's converted in previous paragraph -->.<ref name="Con-122-123" /><ref group=Note>The {{sclass|Aylwin|destroyer|4}} is considered a part of the {{sclass|Cassin|destroyer|4}} by ''Conway's All the World's Fighting Ships 1906–1921'' (p. 122), but is classed separately by the United States Navy. See, for example, {{cite DANFS | author = Naval History & Heritage Command | author-link = Naval History & Heritage Command | url = http://www.history.navy.mil/research/histories/ship-histories/danfs/a/aylwin-ii.html | title = Aylwin (Destroyer No. 47) ii }}</ref> The ''Cassin'' class, the first of the thousand tonners, displaced about a third more than the preceding {{sclass|Paulding|destroyer|4}}.<ref name=Con-122-123 /> The introduction of the thousand tonners led to the ''Paulding''s and other older, smaller displacement destroyers of previous classes to be dismissively called "flivvers",<ref name=Con-121 /> a nickname also commonly applied to the [[Ford Model T]].<ref>Cashman, p. 278.</ref><ref group=Note>According to Cashman (p. 278), a flivver—a [[portmanteau]] of "for the liver"—was any small, inexpensive automobile that shook the liver while in motion.</ref>

[[File:USS Melville (AD-2) and destroyers in World War I.jpg|thumb|left|''O'Brien'' class member {{USS|Ericsson|DD-56|2}}, between the closely related {{sclass|Tucker|destroyer|0}} ships {{USS|Jacob Jones|DD-61|2}} ''(left)'' and {{USS|Wadsworth|DD-60|2}}, is moored by destroyer tender {{USS|Melville|AD-2|2}} at [[Queenstown, Ireland]], in 1917.]]
The ''O'Brien'' class was the third of the five classes of "thousand tonners". The earlier ''Cassin''- (DD-43 to DD-46) and ''Aylwin''-class (DD-47 to DD-50) ships were about the same length as the ''O'Brien'' ships and all had median displacements in the range of {{convert|1020|-|1050|LT|MT}}; the later ''Tucker''- (DD-57 to DD-62) and ''Sampson''-class (DD-63 to DD-68) ships were about {{convert|10|ft|m}} longer and had median displacements of {{convert|1090|-|1100|LT|MT}}. All five classes were armed with four 4-inch guns, but the torpedo size and complement varied. All were equipped with four twin torpedo tubes loaded with eight torpedoes except for the ''Sampson''s (which had four triple tubes carrying twelve torpedoes), but the ''Cassin''  and ''Aylwin'' classes were armed with {{convert|18|in|mm|0|adj=on}} torpedoes. The ''O'Brien'' ships were the first armed with the new 21-inch Mark 8 torpedoes; the ''Tucker'' and ''Sampson'' ships also used the 21-inch torpedoes. The ''Sampson''s were the only group originally equipped with anti-aircraft guns, a pair of [[QF 1 pounder pom-pom|{{convert|1|pdr|adj=on}} guns]] with a [[caliber]] of {{convert|37|mm|in|2|abbr=on}}.<ref name=Con-122-123 />