Thats how its been since WW2, USA has ruled the waves to allow free trade
Deficit financed trade, everyone was happy till one day the US debt bill getting too large so the model running since WWII will have to change.
Looks like nobody happy with those changes as they are coming a bit fast for most.
How will autonomous ships fare when USN not ruling the waves?
Somali type action everywhere?
Ships will just disappear en route?
“Somali type action everywhere?”
The ingenuity of hackers will rule the waves.
What would “Somali type pirates” do with a ship when it is stopped dead in the middle of the ocean?
They don’t have a crew to ransom, or force to take the ship to port.
With no accessible control functions, how do they get the ship moving?
There is no stores to steal and the cargo may be liquid or dry bulk.
Even if boarded by pirates and not moving the ship will still be electronicly traceable.
BTW; Access to the propulsion equipment and control system will likely be behind sealed doors, not easily accessible to anybody who board with ill intent, whether by skiff alongside, or by helicopter from above.
Hacking would be a larger potensial problem.
But I’ll assume that the people who develop the systems for such ship are reasonably digitally littereate and have ways to mitigate hacker attack.
Yes there will be somebody trying to take over control, whether a “neard from his darkened bedroom”, or more professional entities under government control.
Those who life long enough will see how it pans out. It is in any case not an immediate treat to shipping. (There are enough of those at the moment)
An ex tuna seiner with helicopter will do. The high value light cargo is normally on the top tier of containers. money to the right folk ensures knowledge of boxes with the expensive stuff are known. Battery powered angle grinders will unlock most things and a bit of plastic and a detonator will open anything else,
I thought you were talking of "Somali type pirates”, not US navy type piracy. 
Its just the way things are . When the reward is far greater the than the returns offered for catching tuna and the chances of getting caught are slim why not. For 100 years the Royal Navy provided freedom of navigation. Norway had a very large merchant navy and didn’t need a large navy to protect it. It is a bit like the police on the beat and a camera on a street lamp. Which gives you a greater sense of security?