The Italian occupation in Libya started in 1911 and lasted until the Second World War, even if it was often fought by the local population.
You can find the history of Italian plates in Libya used until 1936 in the page about the Italian East Africa: to cut a long story short at the beginning there were the plates of Servizio Militare with a leading T (Tripolitania), as you can see in the first picture; later, from the end of 1920s to 1935, plates similar to the Italian, with white digits on black, with the words TRIPOLI (Tripolitania) or CNA (Cirenaica, CNAICA according to the "Manuale del Turismo" of 1934 of Touring Club Italiano) were in use and you can see one of them in the second picture.
In 1937 the two colonies of Tripolitania and Cirenaica were joined together, also for the new way called "Litoranea Libica" that ran from one to the other, in the new colony called Libya:the new plates were exactly like Italian plates, but with the print "Libia X", where X showed the origin of the plate, according to the table below (pictures number 3 and 4: front and rear from Tripoli). These plates had a special official seal that was different from the Italian one: click here to see a picture (thanks to Luca Maiorano who sent it to me).
Picture 1: 1913-1930(?) - Servizio Militare
Picture 2: 1930(?)-1935 - Tripoli
Picture 3: 1937-1943 - Libia (front)
Picture 4: 1937-1943 - Libya (rear)
Daniele Cacozza wrote me that between 1939 and 1940 there were
probably some more plates that were very similar to Italian plates of that time. They had the following codes:
TL for Tripoli, BE for Bengasi, DE for Derna and MU for Misurata. So far I haven't found anything else about all
this plates and for this reason I'm not even sure that they were issued.
Moreover there was probably one more plate with the code HO that was for the town of Hun (in many cases that same town is names Hon), the administrative center of the "Military Territory of the Southern Libya". Anyway Guglielmo Evangelista told me that according to the guide of Touring Club of that time the road to Hun was completed in 1939 and so it's strange that the plates were issued before the road was available, but they could be issued for the first time in that year. Moreover on the Royal Decree of April the 3rd, 1937, it's written that "for the autovehicles in the southern territory will be used plates according to the rules of the General Governor", so it's likely that special plates were issued of that region, though I don't know anything else about them.
There were also some special plates issued for the vehicles of the government, as shown in the picture number 5: these plaes had the print "Libia Gov." followed by a serial number. Anyway, at the present time I don't know when (the picture was taken in 1938) and for which kind of vehicles they started being issued. In the web site you can also find the full picture I took the detail of the plate from, looking in the old photo gallery (picture number 30).
Picture 5: Government
Regio Corpo Truppe: in 1914 two different corps were created, one in Tripolitania and the other in Cirenaica, named "Regio Corpo Truppe Libiche". At the beginning, as said, they were independent and each of them had its own vehicles, but later, in 1935, they were joined together. The pictures number 6 and 7 show the plates of this corps: the first of them has got the letters RCTL (Regio Corpo Truppe Libiche) followed by a number and the second has got the letters RCTC (Regio Corpo Truppe Coloniali). At the present time I don't know much about both these plates, if the two corps had different plates before the union or which of them was issued before and which later. Guglielmo Evangelista suggested that it's likely that the letters RCTL were used until 1937 to distinguish the corps from similar corps created in Eritrea and Somalia. Later, in 1937 these last two were canceled and so the letters RCTC could be used, without any doubt.
Picture 6: Regio Corpo Truppe Libiche
Picture 7: Regio Corpo Truppe Coloniali
Carabinieri: also Carabinieri worked in Libya and they had their own special vehicles. I don't know much about them, but I found two images (pictures number 8 and 9), though the quality is very poor, of motorcycles with the plates with the letters CC.RR. on the first line, followed by the full name of the town on the second line (the pictures show Tripoli and Bengasi, but it's likely that there were also other towns) and then the number with the symbol of fascio. If you are interested, you can find the full picture I took the plate of Bengasi from in the old photo gallery (picture number 29).
Pictures 8 and 9: Carabinieri (Tripoli and Bengasi)
I want to thank so much Roberto Pola for the first picture, Marcello Taverna for the second that was taken from the magazine "L'auto italiana" of May the 5th 1939, Daniele Cacozza for the third, taken from the book "L'Italia è piccola?" by Francesco Ogliari, and Ernesto Vitetti for the last four images. The picture number 4 is taken from the book "A century of plates" and the picture number 5 is taken from the book "Le fuoristrada Fiat" written by Alessandro Sannia.