The Royal Navy of Oman had 4,200 men in 2000, and is headquartered at Seeb. It has bases at Ahwi, Ghanam Island, Mussandam and Salalah. In 2006, Oman had 10 surface combat vessels. These included two 1,450-ton Qahir-class corvette corvettes, and 8 ocean-going patrol boats. The Omani Navy had one 2,500-ton Nasr al Bahr (L2) LSL (240 troops, 7 tanks) with a helicopter deck. Oman also had at least four landing craft. Oman ordered three Khareef-class corvette corvettes from the VT Group for £400 million in 2007. They are being built at Portsmouth. In 2010 Oman spent US$4.074 billion on military expenditures, 8.5% List of countries by military expenditure share of GDP. The sultanate has a long history of association with the British military and defence industry. According to SIPRI, Oman was the 23rd largest arms importer from 2012-2016.
Question: How many surface combat vessels, landing craft, and tanks does the Oman Navy have?
Answer: 21