Why Britain uniquely needed a carrier maintenance ship

If Unicorn was so useful, why did other navies not copy it directly?

Britain faced a distinctive need to support a Pacific carrier force far from its home industrial base, while its likely opponents operated closer to theirs.

A British carrier force heading to the Pacific faced very long routes around South America, through the Panama Canal, or through the Mediterranean and Indian Ocean. Unlike Japan or the United States, Britain expected to operate at immense distance from its main shipbuilding and aviation infrastructure. Unicorn addressed that geographic logistics problem. The ship was a response to Britain's global basing geometry, which explains why other navies did not need an exact copy in the same period.