New Delhi, June 14 -- BERLIN - The soldiers who would eventually crew the tank that France and Germany set out to build together in 2017 have not yet enlisted in their respective armies. By the time that tank - or its substitute - rolls off a production line, some of them may have retired. That timeline, already straining the patience of every defense contractor involved, came under fresh pressure this week when Armin Papperger, the chief executive of German defense group Rheinmetall AG, said publicly what insiders had been murmuring for months: France may simply walk away.

the long-delayed Franco-German program to replace the German Leopard 2 and the French Leclerc battle tanks. His words landed within days of a separate announcement th...