Notes:
On Wednesday, 30 May 1951, the Indianapolis 500's three slowest qualifiers were Walt Brown (131.907 mi/h), who started from the 13th spot on the departing grid, Cecil Green (131.892 mi/h), who with 200 miles down even led the race, and the rookie Bill Mackey (131.473), the 33rd and the slowest qualifier. Exactly two months later, sadly all three would be dead.

The oldest of the trio was Massapequa, New York, veteran Walt Brown, 40, three times an Indy 500 starter and once a seventh place finisher, in 1947 when he drove Milt Marion's Permafuse Special, a pre-war Alfa Romeo 8C-308 Grand Prix car. A Springfield, New York, native, the five foot, 11 inch Walt Brown was a former bank employee and the brother of a priest. Nicknamed as "Gentleman Walt Brown", he made his debut at the age of 19 on the half mile board track in Woodbridge, New Jersey, waiting until 1939 before earning his first auto race win, in a 30-lap sprint main at Essex Junction, Vermont. During the World War II he served at the Grumman aircraft plant on Long Island.

Walt Brown had been racing for almost 20 years, making 42 Champ Car starts and recording one win, in the 1948 Langhorne 100-mile championship race, driving the same Kurtis-Offy which would win Indianapolis in 1950, driven by Johnnie Parsons.

On Sunday, 29 July 1951, Walt Brown was warming up his car in the "Indianapolis Sweepstakes", an American Automobile Association National Championship 50-lap race - albeit without awarding points - at the half-mile Williams Grove Speedway, in Mechanicsburg, Pennsylvania. He had wanted to drive at the Grove the tan and silver colored Federal Engineering KK3000-Offy he had raced that year at Indianapolis, but the car was not entered in the event. He was at the wheel of the Offy-powered Wetteroth chassis called "Jack Robbins Special", built by Curley Wetteroth in 1938. It had been the 1941 Indy 500 winning car, as the "Noc-Out Hose Clamp Special", co-driven by Mauri Rose and Floyd Davis.

On the approach to the second turn, Walt Brown's car went into a slow tumble-and-flip. Seriously injured in the crash, he was rescued but died soon after arrival at nearby Carlisle Hospital.

After the accident, the race was not stopped and Troy Ruttman in the Agajanian Grant's Kuzma-Offy, eventually was the winner.

Walt Brown was survived by his wife Jane, whom he had married in 1942, and their adopted daughters Bonnie and Wendy. He is buried in St. Charles Cemetery in East Farmingdale, Suffolk County, Long Island, New York. He lies in an unmarked grave in the Hausheer family's plot.

That same Sunday, the two other veterans of the 1951 Indianapolis 500, Green and Mackey, lost their lives in separate accidents during a qualifying session for a round of the American Automobile Association Sprint Car Championship at the Winchester Speedway in Indiana.

Because of the three speedway drivers' fatal accidents, that day, Sunday, 29 July 1951, shook the American post-war racing scene, becoming known in the motorsports media of the time as "Racing's Black Sunday". The night prior to Black Sunday, three spectators were killed at a stock car race at Mount Hawley Speedway in Illinois.

• U.S., World War II Draft Cards Young Men, 1940-1947[ DOB 30 Dec 1910].
• Pennsylvania, U.S., Death Certificates, 1906-1968[ DOB 30 Dec 1910].
• Book "The International Motor Racing Guide", by Peter Higham, David Bull Publishing, Phoenix, United States, ISBN 1-893618-20-X.
• Book "Grand Prix Data Book 1997", by David Hayhoe and David Holland, 3rd. edition, Duke Marketing, Douglas, Isle of Man, United Kingdom, 1996, ISBN 0-9529325-0-4.
• Book "The History of America's Speedways, Past & Present", by Allan E. Brown, third edition, first printing, November 2003, by Allan E. Brown, America's Speedways, Comstock Park, MI, United States, ISBN 0-931105-61-7, page 642.
• Book "Indianapolis 500 Chronicle" by Rick Popely with L. Spencer Riggs, Publications International Ltd., Lincolnwood, IL, 1999, ISBN 0-7853-2798-3.
• The Wilson Howard Davis Archives.
• Magazine Open Wheel, issue of July 1985, pages 80/84.
• Newspaper Miami Daily News (Miami, FL, United States), issue of Monday, 30 July 1951, article "3 Drivers, 2 Spectators Killed Over Week-End", page 2-B, retrieved by website http://news.google.com/newspapers .
• Website Helpline Database, page http://www.helplinedatabase.com/hospital-us/pennsylvania-carlisle.html .
• Website Motorsport.com, chapter Statistics, Champ Cars, research by Phil Harms, page http://www.motorsport.com/stats/champ/data/ch195116.pdf .
• Website Motorsport.com, page http://www.motorsport.com/stats/champ/qrace.asp?C=CH5116 .
• Website Celebrate Today, "Celebrity Automobile Accidents", page http://www.celebratetoday.com/autoceleb.html [M1].
• Website Champ Car Stats, page http://www.champcarstats.com/year/1951.htm .
• Website Champ Car Stats, page http://www.champcarstats.com/drivers2/BrownWalt.htm .
• Website AUTOSPORT → Forums → The Nostalgia Forum, thread "Speed's Ultimate Price: The Toll", page 45, posting by "Buford", message http://forums.autosport.com/index.php?showtopic=9705&view=findpost&p=1883987 .
• Website Find-A-Grave: Walter C. “Walt” Brown.
• E-mail by Andrew McPhee, dated 03 March 2004, citing [M1].
• E-mail by Rick Kelly, dated 11 June 2004.
• E-mail from Steve Estes, dated 12 August 2009.
• E-mail by Carlo Fertitta, dated 11 October 2023 (two messages).