Europe’s armament cooperation rests on a simple economic bargain: several states share the cost of developing, qualifying and supporting a system that each of them would struggle to afford alone. The bargain is made at one moment and lived over decades, and the states that signed it rarely stay still. Governments change, threat assessments shift, budgets expand or contract, and a partner that once wanted sixty aircraft decides it needs fifty-three, or declines to join the next phase of a helicopter upgrade, or walks away from an armoured vehicle programme months after joining it. Each of these moves is usually described with a single number, often the headline value of the programme or of the national share, as if leaving or shrinking a commitment simply removes that sum from the public accounts. It does not. Some spending disappears, some survives as compensation, some is pushed into financing instruments that are repaid years later, some lands on industry, some is absorbed by the partners that remain, and some reappears as delay. Which of these happens depends on how far the commitment had matured when the change came, and on the instruments negotiated to deal with it. This analysis follows three European cases that show the full range: the Tiger Mk III upgrade, where a programme envelope has been mistaken for an order book; the A400M, where two German reductions left a documented trail of redistributed cost; and Slovenia’s departure from BOXER, the clearest public price of an early exit.