The Aurora is a uniquely named research vessel. Which sentence correctly adds its launch year?
The Aurora which was launched in 2018, maps the seabed.
The Aurora, which was launched in 2018, maps the seabed.✓Correct answer
The Aurora, that was launched in 2018, maps the seabed.
The Aurora which was launched in 2018 maps the seabed.
Explanation
The vessel is already identified by name, so which was launched in 2018 is extra information enclosed by commas. The version using that is tempting, but non-defining relatives do not allow that after the comma.