Bulk Rename Utility

Hey Guys and Girls,

I wanna switch parts of the name on other places inside the filename.

I got this list FE:
st_178542_20150601
st_178543_20150301
st_178544_20150101
st_178545_20150701
st_178546_20150801
st_178547_20150901
st_178548_20151001

now I want this:
178542_st_20150601
178543_st_20150301
178544_st_20150101
178545_st_20150701
178546_st_20150801
178547_st_20150901
178548_st_20151001

can anyone help me?

If not, I will use AHK to get the output, but this would need more time.

Thx 4 fast requests

Sincerley
Heiner