New Delhi, June 13 -- Modi landed in Nice on Friday to begin a six-day European tour that will test whether India can close the largest defence deal in its history. The centrepiece is a government-to-government agreement for 114 Dassault Rafale fighter jets, worth an estimated $39 billion. India issued a formal Letter of Request last month and Air Chief Marshal A.P. Singh flew to France in early June for preparatory talks with Dassault Aviation and missile-maker MBDA. But the deal is stuck on a technical fight over a document called the Interface Control Document, and neither side has budged.

operational sovereignty over mission systems is not negotiable.

Under the proposed structure, 18 aircraft would be delivered off the shelf from Da...