What do B-2 bombers and nuclear submarines have in common? Both cost about the same and both require periodic, and expensive, refurbishment. The U.S. B-2 bomber is the most expensive warplane ever to enter service. The 21 that were built ended up costing over $2 billion each. About half of that was development expense. At the time these aircraft were built (in the 1990s), they cost as much as a major warship. The B-2 has similar needs, including periodic (every seven years), lengthy (13 months) refurbishment (programmed depot maintenance, or PDM). Most of the PDM is devoted to refurbishing structural...