This paper addresses the need for reliable multicast (RM) network support for the class of distributed virtual simulations (DVS) that operate with human participants who experience a virtual representation in real time, for example DIS and real-time HLA federations. The need for RM in DVS is explained. The state of reliable multicast networking is explained and typical mechanisms for providing it are described. There is no general solution to RM; all existing RM protocols take advantage of some aspect of their application domain for successful function. Aspects of the DVS domain that lend themselves to providing RM are described, along with an approach to RM for DVS that has been prototyped successfully in the Selectively Reliable Transport Protocol (SRTP). The workings of SRTP are described, including its application to DIS and real-time HLA. SRTP enables efficient use of network-level multicast, and as such represents an advance over the multicast emulation that is used in the Run Time Infrastructure (RTI) created for the Synthetic Theater of War (STOW). In conclusion, ongoing work and potential future improvements to SRTP RM are described.