Looking for movie title, movie was made probably in 1940's or 50's, is about
6 or 7 brothes growing up together who all enlist in the Navy and get on the 
same ship, the ship goes down killing all of the brothers.  The
government passes a new law that forbids brothers to be on the same
ship at time of war.

Hi rick062,

The movie you are looking for is called "The Fighting Sullivans", also
known as "The Sullivans".

"The wartime forerunner of the story told in Saving Private Ryan
(1998) is this emotionally gripping depiction of the Sullivan boys of
Waterloo, Iowa. Amid all the tales of personal tragedy in WW II, this
one stands out. The five inseparable brothers enlisted together after
Pearl Harbor and were all assigned to a battleship that ended up at
Guadalcanal--where all five brothers died in action. A moving tribute
to those who gave their lives in the last world war."
 
Rotten Tomatoes: The Fighting Sullivans (1944)
http://www.rottentomatoes.com/m/fighting_sullivans/about.php


The movie is available for purchase at Amazon:
http://www.amazon.com/exec/obidos/tg/detail/-/B00000F06S


More on the Sullivan Brothers:

HomeOfHeroes: The Brotherhood of Soldiers At War
The Sullivan Brothers - George, Frank, Red, Matt & Al
http://www.homeofheroes.com/brotherhood/sullivans2.html

Anomalies-unlimited
http://www.anomalies-unlimited.com/OddPics/Sullivans.html


Search criteria:
movie brothers navy ship sinks
movie "sullivan brothers" 
"the fighting sullivans"

I hope this is helpful. If you have any questions regarding my answer
please don?t hesitate to ask before rating it.

Best regards,
Rainbow

Minor note: Juneau was a light cruiser, not a battleship.