The ultra-short bunch is the key for producing strong terahertz coherent synchrotron radiation (CSR) and some other applications. A study is being conducted at MIT-Bates South Hall Ring to get 1 mm or shorter electron bunch length. A set of low momentum compaction lattice configurations have been designed. In first beam experiment in 2004, two of these configurations were successfully commissioned in which the momentum compaction was reduced by two orders of magnitude. About 1 mm rms bunch length was measured with a streak camera. It has been demonstrated that this storage ring machine has a great degree of flexibility and potential as an ideal test bed for various advanced beam physics studies.