Detailed Instructions: Generate a correct and concise answer for the question based on the words in the context.
Problem:Context : Works No. 174 started a modernization programme for the ZSU-57-2 in parallel with the beginning of its serial production in 1957, but this programme was rejected due to the development of new radar-guided SPAAGs armed with small-bore autocannons and another tracked chassis.
Question : What was the year ZSU-57-2 entered service?
Solution:
1957