When I started work at Cambridge in 2002 our central supercomputer was being replaced with a cluster of Sun Fire E15K machines with a fancy interconnect - it topped out at position 199 on the top500 list
https://www.top500.org/list/2003/06/?page=2 with a 300 core configuration. It looks like they never managed to get the whole thing working as a single cluster since the other two thirds of the installation had positions 200 and 201! (The Nov. 2002 top500 list has it in 6 x 144 core shards.) Here’s a news item about it:
https://www.cnet.com/news/sun-expands-supercomputer-effort/The big benchmarks in this lovely thesis were run on one of the E15K supercomputer boxes :-)