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Defense industries do source some components from overseas (for example, the 120mm cannon on the M1A2 Abrams MBT) and do sometimes outsource components from dated domestic systems (like the F/A-18 parts you noted), but are much much more resistant to such things than most industries. Such outsourcing also affects relatively few engineers, as the components themselves are designed and tested in the US - most of the domestic losses are in manufacturing. This is often a result of intentional diplomatic efforts by the US government (who really want us exporting military equipment), or a result of extranational laws requiring shared manufacturing.</p>
<p>Compare this to non-defense manufacturers like Apple - do they make ANYTHING in the US?</p>