Highlights from the 56th running of the Indianapolis 500

This May 27, 1972 image provided by Indianapolis Motor Speedway shows Jim Nabors singing "Back Home in Indiana Again" before the Indianapolis 500 auto race at Indianapolis Motor Speedway in Indianapolis, Ind. (IMS via AP) (The Associated Press)

FILE - In this May 27, 1972 file photo, Mark Donohue hugs his mother, Zilly, after he won the Indianapolis 500 auto race at Indianapolis Motor Speedway in Indianapolis, Ind. (AP Photo/File) (The Associated Press)

RACE: 56th Indianapolis 500

DATE: May 27, 1972

WINNER: Mark Donohue

AVERAGE SPEED: 162.962 mph

WHAT HAPPENED: Gary Bettenhausen led 138 laps until his car suffered ignition trouble. His teammate, Donohue, led only the last 13 laps to win the first of team owner Roger Penske's 16 Indy 500 victories.

NOTABLE: Tony Hulman asked Jim Nabors to sing "Back Home Again in Indiana" during the pre-race ceremonies, and Nabors did so without rehearsal, beginning a 36-year tradition with Nabors performing nearly every year from 1972 to 2014. The 1972 race also was the first since 1962 to have an all-American lineup.