The Air Force's fleet of five Hercules C-130 planes have been New Zealand's tactical airlift aircraft since 1965 - that's more than half a century.

When these planes were delivered brand new, Keith Holyoake was prime minister, the Vietnam War was waging, Auckland Airport hadn't yet opened, men hadn't yet landed on the moon, and daily steam train services were operating between Auckland and Wellington.

Long story short: they're old.

Last month's Defence Force white paper concluded the Hercs need to be replaced, as part of a $20b 15-year plan to upgrade and modernise New Zealand's military.

There's still a few more years left in the Hercs, but they'll need to be retired sometime between 2020 and 2022. That sounds like a long way away, but in defence, and aviation generally, procurement needs to be planned in advance.

So, what are the options? Which aircraft are being eyed up by the top brass? Here's a few that are on the list.