That's a good question to which I unfortunately don't have an answer. I don't have any information on that specific example.
However, the fact that a department doesn't spend all the amounts that are allocated to it isn't necessarily a good thing. As a taxpayer, I prefer that a department not spend all its votes rather than waste them, but one can definitely conclude that a department as large as National Defence is capable of properly planning its capital spending and balancing its budgets, especially its capital budgets and spending amounts.