Defense Department contracting is a very lucrative business where companies are paid billions of dollars each year. When the stakes are that high, people get creative in their fraud schemes. Sometimes sham companies are set up in order to give the impression that subcontractor costs are higher than what they actually are. Sometimes companies submit false invoices for payment. Sometimes companies use subgrade materials in order to increase their profit margins.
These examples of defense contractor fraud reflect the high losses to the government.
https://qz.com/1755722/defense-department-has-lost-875-million-to-shell-company-scams/
https://fas.org/blogs/secrecy/2019/05/defense-contracting-fraud/