What are these things?

I have seen two trains recently that have stumped me. Each was about a mile long and was composed entirely of flatcars marked AVXX. Each car had 4 battleship grey containers (for lack of a better word) that looked like either dumpsters with side doors or really big transformers. Each was marked AVU. Does anyone have any idea what these things were? Thanks

Is this what you’re looking at… The garbage train?

Sorry for the long link…

http://naphotos.nerail.org/showpic/?2002011215491015430.jpg:bysearch:garbage:SEARCHTYPE=ADVANCED&PAGE=2&SEARCHSTRING=garbage&BOOL=ANY&RAILROAD=ANY&PHOTOGRAPHER=ANY&PHMS=&PHDS=&PHYS=&PHME=&PHDE=&PHYE=&POMS=&PODS=&POYS=&POME=&PODE=&POYE=&RES=LONG

PS…are you the real Grandpa Pettibone of Naval Aviation safety lore???

By heck, that is it!!! I never saw one of those come through here and have seen 2 in the last week… Thanks. I had all sorts of exotic ideas about what they were and thet are indeed dumsters! mNo, I ain’t the original old curmudgeon, but getting close. Thanks again