Background: From 1958, the Union Castle shipping line gradually reduced its service calls to the island. Curnow Shipping, based in Avonmouth, replaced the Union-Castle Line mailship service in 1977, using the RMS (Royal Mail Ship) St Helena.
Question: What year was Union-Castle Line mailship replaced?
Answer:<extra_id_0>.
<extra_id_0> 1977<extra_id_1>