The Composite Share Ratio (CSR) is the financial contribution paid by each partner nation to common production, support and follow-on development activities for the collaborative partnership that jointly manages the international Joint Strike Fighter programme. This is a non-discretionary contribution which the UK committed to with other partner nations when signing the production, sustainment and follow-on Development Memorandum of Understanding in 2006. It buys joint assets such as production tooling and common technical services which enable the aircraft to be both manufactured and supported. CSR is calculated based on the total number of aircraft being procured by each nation.
At publication of the National Audit Office major Projects Report 2013, the CSR portion of the £999 million approved cost for the production of four aircraft, including initial spares provision, risk, concurrency, necessary programme and support arrangements and long lead items was £230.4 million. The last financial year of this CSR figure is based on an estimate which is subject to minor change and will be published in the National Audit Office Major Projects Report 2014. This CSR figure will be a reduction and not an increase.