Conductive materials such as water are not going to be an effective medium for an EMP. It's possible, but instead of the effects we think of in regards to land-based or air-born EMPs, effects such as the downing of electronics on a massive scale, an underwater EMP will dissipate too quickly and the energy cannot be focused as the water's conductivity will spread it in an amorphous pattern. It makes for good movie material, but in real life such a scenario is fiction.
Thanks for the clarification.
What about firing a device which could attach itself to the Russian submarine and fry it in an electrical eel type effect?