CREATE TABLE table_53897 ("Name" CLOB, "Original name" CLOB, "Commissioned" CLOB, "Final decommission" CLOB, "Fate" CLOB)

When was the ship originally named sachem finally decommissioned?
SELECT "Final decommission" FROM table_53897 WHERE "Original name" = 'sachem'
SELECT "Final decommission" FROM "table_53897" WHERE "Original name" = 'sachem'