The first internationally recognized alphabet was adopted by the ITU in 1927. The experience gained with that alphabet resulted in several changes being made in 1932 by the ITU. The resulting alphabet was adopted by the International Commission for Air Navigation, the predecessor of the ICAO, and was used in civil aviation until World War II. It continued to be used by the IMO until 1965:

Amsterdam Baltimore Casablanca Denmark Edison Florida Gallipoli Havana Italia Jerusalem Kilogramme Liverpool Madagascar New_York Oslo Paris Quebec Roma Santiago Tripoli Upsala Valencia Washington Xanthippe Yokohama Zurich

Military alphabets before 1956:
United Kingdom United States
Royal Navy Western Front slang
or “signalese”
RAF phonetic alphabet US phonetic alphabet
1914–1918 (WWI) 1924–1942 1943–1956 1941–1956
Apples
Butter
Charlie
Duff
Edward
Freddy
George
Harry
Ink
Johnnie
King
London
Monkey
Nuts
Orange
Pudding
Queenie
Robert
Sugar
Tommy
Uncle
Vinegar
Willie
Xerxes
Yellow
Zebra
Ack
Beer
Charlie
Don
Edward
Freddie
Gee
Harry
Ink
Johnnie
King
London
Emma
Nuts
Oranges
Pip
Queen
Robert
Esses
Toc
Uncle
Vic
William
X-ray
Yorker
Zebra
Ace
Beer
Charlie
Don
Edward
Freddie
George
Harry
Ink
Johnnie
King
London
Monkey
Nuts
Orange
Pip
Queen
Robert
Sugar
Toc
Uncle
Vic
William
X-ray
Yorker
Zebra
Able/Affirm
Baker
Charlie
Dog
Easy
Fox
George
How
Item/Interrogatory
Jig/Johnny
King
Love
Mike
Nab/Negat
Oboe
Peter/Prep
Queen
Roger
Sugar
Tare
Uncle
Victor
William
X-ray
Yoke
Zebra
Able
Baker
Charlie
Dog
Easy
Fox
George
How
Item
Jig
King
Love
Mike
Nan
Oboe
Peter
Queen
Roger
Sugar
Tare
Uncle
Victor
William
X-ray
Yoke
Zebra

In military use British and American armed forces each developed their phonetic alphabets before both forces adopted the ICAO alphabet in 1956. British forces adopted the RAF phonetic alphabet, which is similar to the phonetic alphabet used by the Royal Navy in World War I. The U.S. adopted the Joint Army/Navy Phonetic Alphabet from 1941 to standardize systems amongst all branches of its armed forces. The U.S. alphabet became known as Able Baker after the words for A and B. The UK adapted its RAF alphabet in 1943 to be almost identical to the American Joint-Army-Navy (JAN) one.

After World War II, with many aircraft and ground personnel drawn from the allied armed forces, “Able Baker” continued to be used in civil aviation. But many sounds were unique to English, so an alternative “Ana Brazil” alphabet was used in Latin America. But the International Air Transport Association (IATA), recognizing the need for a single universal alphabet, presented a draft alphabet to the ICAO in 1947 that had sounds common to English, French, and Spanish. After further study and modification by each approving body, the revised alphabet was implemented on 1 November 1951 in civil aviation (but it may not have been adopted by any military):

Alfa Bravo Coca Delta Echo Foxtrot Golf Hotel India Juliett Kilo Lima Metro Nectar Oscar Papa Quebec Romeo Sierra Tango Union Victor Whisky Extra Yankee Zulu

Immediately, problems were found with this list. Some users felt that they were so severe that they reverted to the old “Able Baker” alphabet. To identify the deficiencies of the new alphabet, testing was conducted among speakers from 31 nations, principally by the governments of the UK and the US. Confusion among words like Delta, Nectar, Victor, and Extra, or the unintelligibility of other words under poor receiving conditions were the main problems. After much study, only the five words representing the letters C, M, N, U, and X were replaced. The final version was implemented by the ICAO on 1 March 1956, and was adopted before 1959 by the ITU, because it appears in the 1959 as an established phonetic alphabet. Because the ITU governs all international radio communications, it was also adopted by all radio operators, whether military, civilian, or amateur (ARRL). It was finally adopted by the IMO in 1965. In 1947 the ITU adopted the compound number words (Nadazero Unaone, etc.), later adopted by the IMO in 1965.

Letter Code word Pronunciation IPA from ICAO
A Alfa (ICAO, ITU, IMO, FAA)
Alpha (ANSI)
AL FAH ˈælfɑ
B Bravo BRAH VOH ˈbrɑːˈvo
C Charlie CHAR LEE  or
SHAR LEE
ˈtʃɑːli  or
ˈʃɑːli
D Delta DELL TAH ˈdeltɑ
E Echo ECK OH ˈeko
F Foxtrot FOKS TROT ˈfɔkstrɔt
G Golf GOLF ɡʌlf
H Hotel HO TELL (ICAO)
HOH TELL (ITU, IMO, FAA)
hoːˈtel
I India IN DEE AH ˈindiˑɑ
J Juliett (ICAO, ITU, IMO, FAA)
Juliet (ANSI)
JEW LEE ETT ˈdʒuːliˑˈet
K Kilo KEY LOH ˈkiːlo
L Lima LEE MAH ˈliːmɑ
M Mike MIKE mɑik
N November NO VEM BER noˈvembə
O Oscar OSS CAH ˈɔskɑ
P Papa PAH PAH pəˈpɑ
Q Quebec KEH BECK keˈbek
R Romeo ROW ME OH ˈroːmiˑo
S Sierra SEE AIR RAH (ICAO, ITU, IMO)
SEE AIR AH (FAA)
siˈerɑ
T Tango TANG GO ˈtænɡo [sic]
U Uniform YOU NEE FORM  or
OO NEE FORM
ˈjuːnifɔːm  or
ˈuːnifɔrm
V Victor VIK TAH ˈviktɑ
W Whiskey WISS KEY ˈwiski
X X-ray or
Xray
ECKS RAY (ICAO, ITU)
ECKS RAY (IMO, FAA)
ˈeksˈrei
Y Yankee YANG KEY ˈjænki [sic]
Z Zulu ZOO LOO ˈzuːluː

Courtesy of Wikipedia