A person who knows things that captains aren't privy to wouldn't be a disposable person. That person would have to be higher up in the chain.
When I think of the character Harrison, I see a lone wolf version of Brigadier General Hummel, from "The Rock".
That's because his real name is J
arkness and he works for
Torchwood: outside the government, beyond the police. Fighting for the future on behalf of the human race