Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
The ship SSBergensfjord built before 1973 has what tonnage?

### Inputs:
table_name: table, columns: ['Ship', 'Built', 'In service for NAL', 'Type', 'Tonnage']

### Response:
SELECT Tonnage FROM table WHERE Built < 1973 AND Ship = ssbergensfjord