I was in another forum and someone was asking about COMPANY names in WWII. I threw in the fact that there was NO COMPANY J in WWII. Did ya know that.? They wanted to avoid confusion because the letter "I" looks too much like the letter "J", so they actually skipped it.
Here's more info on that:
The infantry regiment was organized with three battalions, twelve lettered companies (A-M, skipping J), an Infantry Cannon Company (first equipped with two halftrack-mounted 105mm howitzers and six halftrack-mounted 75mm howitzers or guns, and later with a towed short-barrelled 105mm howitzer), an Antitank (AT) Company (initially with twelve 37mm and later nine 57mm AT guns), and a Service Company. The fourth company in each battalion (D, H, M) were heavy weapons companies with sustained fire heavy machine guns and mortars. The regiment and each battalion also had a H&H Company. The regimental H&H Company included a Intelligence and Reconnaissance Platoon, the battalion H&H company included an Amunition and Pioneer (A&P, responsible for light engineering duties and for transporting ammunition forward to the line companies) Platoon and an AT Platoon (initially with four 37mm and later with 3 57mm AT guns).
If you want to read the entire article on army units during WWII, this is a good one:
Army Units in WWII
We must remember the US models most military after European Armies. There is no J in some alphabets, maybe the reason!
Ah, that could be one possible reason too my dear. R Lee Ermey also covered this topic recently on this Mail Call show on the History Channel and he also stated that the reason there was no letter J during WWII was that the letters I and J could be confused and therefore possibly have the potential for disaster. 
R Lee Ermey's Website
Semper Fi
Red Arrow 32nd Division (contained the following)
4 Regiments: 124th,,,125th,,,126th,,,128th,,,
Each regiment contained 3 Battalions
Each Battalion contained 4 Companies
Each Company contained 196-200+ men
cadetat6
Usual Infantry Regt. in ETO: 3 Rifle companies, 1 weapons company, 1 Hdq. Co.
per Bn. 3 Bns per Reg. Rifle Companies were A,B,C, weapons company was D, plus
Hdq Co. for 1st Bn. . 2 Bn. was E,F,G, as rifle companies and H Co. as weapons Co.
plus Hdq Co.. 3rd Bn was I,K,L, as rifle companies, and M Co, as weapons Co. plus
Hdq. Co. . No J company. Many explationations but no actual true answer I know of.
I've created a webpage that explains the organization of a US Infantry Division in WW2. I drew charts to show their command structure.
Here is one of the charts that shows the companies within a Regiment and how they are formed into Battalions. The BLUE numbers represent the number of troops in that unit. NOTE: This only applies to Infantry (not Airborne Infantry) and only WW2 divisions.
The page is still in DRAFT form. I already see that the first Chart and last Chart are switch. You can view this at: US Infantry Division
Steve
Ref: Stauntons Order of battle WW II
Allo Inf. Divisions were square (4 regiments, 2 bridages) until Dec. 8th 1941
By General Order they dropped one regiment. after that date All WWII Infantry Divisions were triangular( 3 regiments)
......... there was NO COMPANY J in WWII. Did ya know that.? They wanted to avoid confusion because the letter "I" looks too much like the letter "J", so they actually skipped it ..........
That actually harks back to the Civil War for the US Army -- and that is why there is no 7th Cavalry Company J memorialized for the Battle of the Little Big Horn.
Yes indeedie-do James. I had posted that above and most people hesitate to believe it. What, no Company J? Yup it was true!
And Joe, yes you are right, four divisions was the thing, then the triangular setup became the norm. Two outfits up front and one in reserve.
We are all on the ball here. What a top-notch crew we have! 