How hard is it to convert an airliner into a patrol aircraft?

Is converting a civilian airliner into a maritime patrol aircraft a straightforward task?

Modern conversions such as the E-7 and P-8 are highly specialised, but a Second World War conversion could be much simpler, adding observation positions, defensive guns, fuel, navigation equipment, and bomb-carrying capacity.

Modern military derivatives of airliners are far more than ordinary passenger aircraft with a few fittings added. The E-7 and P-8 require substantial changes for their customers and missions. Wartime conversions could produce useful patrol capability with observation blisters, guns, extra fuel, better navigation equipment, and the ability to drop bombs. The complexity of a modern sensor aircraft is therefore a poor guide to what an emergency conversion meant in the 1940s.