Tomcat suddenly dies without a whisper

Hi,

We are running Tomcat 5.5 on a powerful VM Server.  MS Sql Server is also
on the VM.  It is fronted by an apache web server on another box.

When under load (heavy but not excessive) we suddenly find tomcat dies,
without any error messages we can find.  Memory looks good.

We are a little perplexed as to where to look next.  Any ideas?

cheers,

David