SOME NOTES ON THE EARLY (1830s-1850/60s) RANK SYSTEM
The reason why Ottoman Turkish ranks appear so complicated is that the Ottoman Turkish military in WW1 were still operating with a very different logic toward ranks and roles, which makes it difficult to directly draw comparisons with typical European military organisation. The reason for this, has to do with the origin of Ottoman military rankings some 70 years earlier (from the 1909–period), on which WW1 ranks were based. Beginning in 1832, with the first establishment of the regular Ottoman Army in the Abdülmecid I period, which was based on a very different and strict hierarchy from that found in contemporary European militaries. Firstly, the officers were grouped according to the traditional titles of nobility, which also corresponded to various military ranks. Thus, ‘PASHAS’ (Generals), ranked above ‘BEYS’ (Colonels), and the ‘AGHAS’ (certain civil and military functionaries in the Ottoman empire), but below ‘KHEDIVES’ (the Royal King of Egypt), and ‘VIZIERS’ (the Ottoman Sultan’s ministers – who were frequently senior generals in the army). The origin of these various grades relates to the early medieval period of the Ottomans. For example, the title of Pasha was distinguished by the number of yak- or horse-tails (three, two and one respectively; a symbol of Turco-Mongol tradition) or peacock tails, which the bearers were entitled to display on their standard as a symbol of military authority when on campaign. Only the Sultan himself was entitled to four tails, as sovereign commander in chief. The lower ranks of officers were addressed as Bey (Majors), or Effendi, (Captains and Lieutenant). A system of rank within the various grades of titles, more in accord with European practices had been introduced during the Abdülmecid I period, however this was not likely to have been immediately recognisable to European observers as the time. This was the introduction of a system of orders, badges and insignia made and issued by the Imperial Mint, which were catalogued in a special Imperial Album (illustrated below). In the Ottoman military rank system, a multitude of various, rank, authorities and military roles was associated with their own particular order, and an examination of the reproduced volume found in ‘Ottoman Medals and Orders’ , indicates about 407 different military ranks, authorities and roles.
C.A. Norman notes (Flaherty, C. (2011) Ottoman Uniforms of the Crimean War. SOTQ. Issue 147 (December): 16-27.) that Ottoman officers almost invariably wore a 'passant' or epaulet loop of gold lace on either shoulder near the sleeve seam, which seems to have served as a mark of officer status (there are no indications that epaulets were ever attached to these, except possibly in some Guard units - In fact epaulettes only indicated a group of general ranks, not individual ones, and were wore on dress-uniform occasions). Apart from these simple devices, generally there is no indication of any system of officer's rank insignia in use in the Ottoman army; both Vanson and Constantin Guys (who were in the Crimean War, and sketched Ottoman soldiers), commented on the apparent lack of any form of rank insignia among the Ottoman officers.
The observation that there was no indication of any system of officer's rank insignia in use is incorrect. However, to the Europeans at the time, the actual insignia being used would not have been recognisable to them. To the casual European observer these various orders, badges and insignia would have appeared as medals, and most likely assumed to be, without understanding these actually conveyed the wearers corresponding military rank. As can be clearly illustrated looking at the period-picture of an Ottoman officer wearing his rank-order (see below):

During the Abdülmecid I period, Crimean War observers (Vanson and Constantin Guys), referred to the officers having the epaulet bridles in gold lace, but not epaulettes attached. The Ottoman practice of not wearing rank is well documented. For instance, it was recorded in WW1 that, “in action there has been a tendency on the part of officers to discard all badges of rank.” (British General Staff. (1995) 1916 Handbook of the Turkish Army. Battery Press, Nashville: 136).