Montebello was a steam oil tanker built in 1920–1921 by the Southwestern Shipbuilding Co. of San Pedro for Union Oil Company with the intention of carrying oil and petroleum products along the West Coast of the United States and Canada as well as between the United States and Chile. In December 1941 the tanker was sunk on one of her regular trips by the . Design and construction Early in 1920 Union Oil Company of California decided to expand their South American business and placed an order for two large tankers of approximately 12,000 tons deadweight with Southwestern Shipbuilding Company. At the time of the tankers were the largest vessels of their kind ever to be constructed in California. The keel laying for both vessels, future SS Montebello and SS La Placentia, was held on 20 April 1920 with over forty Union Oil representatives present at the ceremony. Montebello was the first of these vessels and was launched on 24 January 1921 (yard number 21), with Miss Adelaide Stewart, daughter of William L. Stewart, president of Union Oil, being the sponsor. The tanker was named after Montebello oil fields, a major source of oil for Union Oil Co. The ship was built on the Isherwood principle of longitudinal framing providing extra strength to the body of the vessel. The ship was shelter-deck type, had two main decks and had its cargo space subdivided into eighteen main tanks and ten summer tanks which allowed for the carriage of up to 94,000 barrels of oil. The tanker had a cargo pump room located amidships with specially designed pumps to be able to unload her entire cargo in about twenty hours. In addition, the steamer was equipped with eight throttle reversing steam winches for quick loading and unloading of cargo from shelter deck spaces. She was also equipped with wireless apparatus, had submarine signal system installed and had electrical lights installed along the decks and in crew cabins. As built, the ship was long (between perpendiculars) and abeam, and had a depth of . Montebello was originally assessed at and and had deadweight of approximately 12,500. The vessel had a steel hull with double bottom throughout and a single 3,300 ihp vertical reciprocating quadruple expansion steam engine, with cylinders of ,, and diameter with a stroke, that drove a single screw propeller and moved the ship at up to . The steam for