Ships and seamen within the U.S. Navy can expect to be at sea for months at a time, with eight month deployments becoming the norm often in dangerous locations or the middle of nowhere.
It is impossible to outfit ships with enough provisions for that long a cruise, so underway replenishment have taken on a new level of importance for the Navy.
During an underway replenishment, a supply ship can transport fuel and food to a recipient ship allowing them to stay at sea away from harbor for significantly longer times.
The processes and technical precision behind carrying out an underway replenishment are nothing short of amazing.
Ships partaking in underway replenishment must pull next to each other and match each other’s speeds. Any slight difference in speed or direction could cause a collision.
After the ships have matched each other’s speed and have a set course, both ships fire shot lines to each other.
The shot line, after being successfully shot to the other boat, is connected to a sturdier messenger line. This line has to be pulled across the distance between the ships.
Attached to the messenger line is the iron cabled spanwire. Once fully dragged across the divide between the two ships, the spanwire is clamped into place to ensure stability.
Once everything is securely in place, the underway replenishment line can be towed across the spanwire. The line then slots in perfectly into the nozzle of the receiving ship.
Underway replenishment is a risky manoeuvre, especially if a supply ship is connected to two ships at once. In the event of an emergency, ships are taught to practice emergency breakaway procedures. This will ensure the ships don’t collide, but it could lead to a possible losing of stores.
Below is a video of a ship replenishment operation in action.
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