All popular TLDs are taken, and 56 mio. search results on Google - that's good.
But there've been no noteable domain sales in the past on the term. The only one that's worth noting is defences.com for $1,100 last September. This doesn't look good for a sale on defence.pro, esp. when you keep in mind that all .com, .net and .org are unused.
And I can't imagine what to do with this domain. The .pro extension doesn't make much sense for this term. Any ideas?
All in all, I think that the domain is worthless, or at most very low $xx-$xxx.