Singapore appears to have quietly boosted the size of its F-15SG fleet from 24 aircraft to 40, according to Boeing financial statements, aircraft registration filings, and US congressional reports.
Singapore originally bought 12 F-15SGs - with an option for eight more - under a contract signed in December 2005. In October 2007 the city-state modified this option by buying 12 more to give it a total of 24.
These aircraft have all been confirmed as delivered and have US-type serial numbers running from 05-0001 to 05-0024. Several remain in the United States with the Republic of Singapore Air Force's (RSAF's) 428th Fighter Squadron at Mountain Home Air Force Base (AFB) in southwestern Idaho, while the remainder are active in Singapore with 149 Squadron.
Aircraft operating in Singapore use four-digit serial numbers in the 83xx sequence, starting at 8301, although these do not run consecutively.
In January 2014, several aircraft with new serial numbers - 05-0025, 05-0028, 05-0030, 05-0031, and 05-0032 - were seen at Mountain Home AFB. These had not been previously reported and suggest that Singapore has obtained another batch of eight aircraft.
Meanwhile, a 26 November 2012 letter from the US State Department to House of Representatives Speaker John Boehner under the Arms Export Control Act refers to the "sale, modification, and follow-on support of eight F-15SG aircraft to the Government of Singapore".
Figures released by Boeing show that eight F-15s were delivered to an unspecified customer in 2012.
Boeing financial data also shows that a total of 93 F-15s were delivered from 2005 to 2012. South Korea has confirmed that it received 61 and Singapore that it received 24 for a total of 85, leaving eight unaccounted for in public records.