Another huge factor is the service lifetime of military equipment. There are aircraft that were designed and created in the 1970s that are still in use today.

Another huge factor is the service lifetime of military equipment. There are aircraft that were designed and created in the 1970s that are still in use today. Sure, many of the components and internal systems have been modified and upgraded, but much of the original design is still there and operating. >> a military contract will be for a production run and follow on support. When "follow-on support" has to last for 50 years or more, it makes a big difference.