The largest Royal Navy warship ever to take to the sea, the fleet carrier HMS Queen Elizabeth (R08), has been in the water for six years. This means a drydocking period to check her hull and strip away the trees that are growing upon it.
While based at HMNB Portsmouth, she was assembled over an eight-year period in the Firth of Forth at Rosyth Dockyard from components built in six UK shipyards (way to subcontract the pork!) and has headed back to her place of birth for the work. This means sailing under the three Forth bridges, for which she was specifically designed to pass through the (temporary) lowering of her mast.
Similarly, the Queen Elizabeth-class were designed with just 39-inches of clearance to pass through the lock into Rosyth Dockyard– weather and tides providing.
It’s not the only case of ships being formatted to meet navigational limitations. For generations, the U.S. Navy’s carriers and battleships were limited to fit the 110-foot-wide and 890-foot-long Miraflores lock chambers of the Panama Canal (the waterline beam of the Iowa-class was 108 feet while they were 888-feet long, providing just a foot on each side to squeeze through).
It was controversial to construct the Midway-class of carriers in the 1940s as too big to transit the Canal– a first for the Navy.
Further, to be able to reach the Brooklyn Navy Yard, vessels up to the Forrestal and Kitty Hawk-class conventional supercarriers had an allowance to swing their mast so that could get under the Brooklyn Bridge.
Previous carriers, the Midways, and Essex-classes included could just make it without de-masting.
As could the tallest lattice masts of dreadnought battleships.