user: Question: What is the Entered service date of the H1 Locomotive?
Columns: ['Locomotive', 'Delivered as', 'Entered service', 'Owner', 'Status']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['H1', 'T413', '20 December 1968', 'Pacific National - Rural and Bulk', 'In Service']
SQL:

assistant: SELECT "Entered service" FROM "Table" WHERE "Locomotive" = 'H1';