Saudi Arabia acquired a total of 50 Pilatus PC-9s, with deliveries beginning in 1986. The aircraft formed part of the British–Saudi Al-Yamamah arms deal, which was later investigated over corruption allegations. On 14 December 2006, the UK Serious Fraud Office ended its corruption investigation into the Al-Yamamah deal following diplomatic pressure. Saudi Arabia had threatened to end counterterrorism cooperation; investigators were then seeking access to Swiss banking records. On 30 July 2008, the House of Lords upheld the legality of ending the investigation on national security grounds.