You have killed hundreds of brits, even thousands if you account the Revolutionary war.
Since I had some time to kill I took some of the bigger incidents of friendly fire from US history:
American Revolutionary War:
In the
Battle of Germantown in 1777, a combination of late arrival, poor navigation and overpursuit resulted in
Major General Adam Stephen's men colliding with General
Anthony Wayne's troops. The two American brigades opened fire on each other, became badly disorganized, and fled.
American Civil War:
- During the Battle of Antietam, a Confederate regiment had maneuvered into a gap between two Union regiments and launched a surprise attack during a union advance into a wooded area. The Union regiment hit by the surprise attack hastily began returning fire and unknowingly hit the other Union regiment with musket fire that overshot the Confederate regiment, causing the other Union regiment to return fire in confusion. The two Union regiments had sustained heavy casualties during the lengthy exchange of friendly fire.
- Confederate General Thomas Jonathan "Stonewall" Jackson was wounded as a result of friendly fire in the Battle of Chancellorsville and died eight days later. He and some of his men had been returning, under the cover of night, from an intelligence-gathering mission when a Confederate patrol misidentified them as a Union cavalry scout team.
- During the Battle of the Wilderness, Confederate Brigadier General Micah Jenkins was killed and another Confederate General James Longstreet was wounded when fellow Confederate forces open fire on their convoy who mistook them for Union soldiers on 6 May 1864, four miles from Chancellorsville, Virginia. Longstreet was unable to attend the rest of the Overland Campaign until he had recovered.
1942
21 February - Pilots of the
1st American Volunteer Group (Flying Tigers) strafed retreating Commonwealth forces who were mistaken for an advancing Japanese column during the
Burma Campaign, resulting in more than 100 casualties.
[19]
During the night attack of 12/13 November in the
Naval Battle of Guadalcanal, the already damaged
light cruiser USS Atlanta was fired on by the
cruiser USS San Francisco causing several deaths.
1943
During the Allied Invasion of Sicily,
Operation Husky, 144
C-47 transport planes passed over Allied lines shortly after a German air raid, and were mistakenly fired upon by U.S ground and naval forces. 33 planes were shot down and 37 damaged, resulting in 318 casualties.
[24]
During
Operation Cottage after Allied forces landed on
Kiska island, both US and Canadian forces mistook each other as Japanese and engaged each other in a deadly nighttime firefight. As a result, 28 Americans and 4 Canadians were killed and 50 others injured. There were no Japanese troops on the island two weeks before the Allied forces landed.
1944
July 26, 1944,
USAAF P-47s mistakenly strafed the US 644th Tank Destroyer Battalion near
Perrières, France. 20 men were badly injured but causing no fatalities.
[29]
Major
George E. Preddy, commander of the 328th Fighter Squadron was the highest-scoring US ace still in combat in the European Theater when he died on Christmas Day in Belgium at the time. Preddy was chasing a German fighter over an American anti-aircraft battery and was hit by their fire aimed at his intended target.
Korean War:
- On September 23, 1950, Hill 282 was attacked by 1st Battalion, Argyll & Sutherland Highlanders, part of the British 27th Infantry Brigade in the United Nations force. Having captured it and facing strong North Korean counter-attacks, the Argylls, devoid of artillery support, called in an allied air-strike. A group of F-51 Mustangs of U.S. Air Force's 18th Fighter Bomber Wing circled the hill. The Argylls had laid down yellow air-recognition panels correctly in accordance with that day's planning, but the North Koreans imitated similar panels on their own positions in white. The Mustangs, confused by the panels, mistakenly napalm-bombed and strafed the Argylls’ hill-top positions. Despite a desperate counter-attack by the Argylls to regain the hill, for which Major Kenneth Muir was awarded a posthumous Victoria Cross, the Argylls, much reduced in numbers, were forced to relinquish the position. Over 60 of the Argylls’ casualties were caused by the friendly air-strike.
Vietnam War:
A U.S.
F4 Phantom aircraft dropped a 500 lb (230 kg) bomb on the command post of the 2nd Battalion (Airborne) 503d Infantry, 173d Airborne Brigade while they were in heavy contact with a numerically superior NVA force on 19 November 1967 during the
Battle of Dak To. At least 42 paratroopers were killed and another 45 wounded. Also killed was the Battalion Chaplain Major
Charles J. Watters, who was subsequently awarded the Medal of Honor.
Gulf War:
- An American AH-1 Cobra attack helicopter fired upon US Army Bradley Fighting Vehicles during night operations, killing several US Army soldiers.
- Two American soldiers were killed and six others injured when their Bradley Fighting Vehicle was struck by a Hellfire missile fired by an American AH-64D Apache helicopter during night operations.
- An American A-10 during Operation Desert Storm attacked British Warrior MICVs, killing nine British soldiers and further 11 injured.
War in Afghanistan:
In the
Tarnak Farm incident of April 18, 2002, four Canadian soldiers were killed and eight others injured when U.S. Air National Guard Major Harry Schmidt, dropped a laser-guided 500 lb (230 kg) bomb from his
F-16 jet fighter on the
Princess Patricia's Canadian Light Infantry regiment which was conducting a night firing exercise near
Kandahar. Schmidt was charged with negligent manslaughter, aggravated assault, and dereliction of duty. He was found guilty of the latter charge. During testimony Schmidt blamed the incident on his use of "go pills" (authorized mild stimulants), combined with the '
fog of war'.
[68] The Canadian dead received US medals for "bravery", but no apology.
That was a statement which attempted to illustrate how idiotic your whole "what if" scenario was and still is.
Also, both sides were building a long highway towards each other, which was in preparation for invasion to allow supplies and tanks to move fast.