Probably the most important invasion of Persia by British troops has been the occupation of the Bagdad-Caspian line of communication, actively begun at the first of this year and following the Russian retirement. This invasion seems to have been justified so far as military necessity was concerned, because of the inability of the Persian government to protect its own neutrality. It had the double objective of throwing a barrier across Persia in the way of a possible enemy invasion from the north, and of gaining control of the Caspian sea and cutting off the pan-Turanian movement or invasion into Turkestan and beyond.
Both objectives have been accomplished, and as the British have control of the Caspian it is my opinion that the present military and political situation in Persia and Turkestan is unlikely to change pending decisive results on the Western front, as Turkey’s possible military efforts can at best be but feeble ones in either Persia or the Caucasus without definite and considerable German aid. The control of the Caspian sea has, according to recent developments, been the key to the entire situation in Persia and Turkestan, and as it is now apparently firmly in the hands of the British further developments of importance during the present year seem improbable so far as enemy progress is concerned.
The British had before this time established themselves in Bagdad and shortly after the withdrawal of the Russians became probable [end of 1917] British plans were underway for the occupation of the line from Bagdad across Persia via Kermanshah and Hamadan to the Caspian at Enzeli. A small British detachment with wireless equipment is understood to have been established in Kermanshah as early as the middle of 1917, this place being 304 miles by caravan from Bagdad. After the occupation of Bagdad a railroad was begun by the British running towards the Persian frontier and early this year it had reached the small town of Ruz, sixty miles north-east of Bagdad.
Ruz is not shown on most maps, but may be located as about half way between Shahroban [Shahraban] and Kizil-Robat, which are shown on good maps. With Ruz as base preparations were made for the occupation by British troops of the route across Persia to the Caspian. In January of this year  Major General Dunsterville went into Persia with a small party of hand picked officers. He went as far as the Caspian and returned to Mesopotamia to organize the expeditionary force. Great secrecy was maintained and this expedition into Persia, although officially known as the Dunster force, was known among the military people as the “hush-hush” force, because it was not permitted to be discussed even in Bagdad.
By the middle of June  the British had approximately 2,500 troops in Persia, the force being spread out over the line of communication from Ruz to the Caspian. At this time the Dunster force consisted of parts of one mixed division from Mesopotamia, the thirteenth and the fourteenth divisions. Between Kermanshah and Ruz some Indian battalions [a battalion consists of approximately 1,000 men] were observed, but beyond Kermanshah the troops seemed to be all British with the exception of parts of two battalions of Ghurkas [Indians belonging to the mixed division mentioned above], brought in for special work, and who are considered equal to British troops in being able to stand cold weather which they will experience in Persia and on the Caspian during the coming winter. The Ghurkas are considered to be the best fighters in the Indian army.
The latter part of August there were possibly 10,000 troops along the Bagdad-Caspian line, in addition to 5,000 at that time in Baku. As far as I was able to observe there were six complete battalions of British infantry along this line, one battalion of British cavalry, and nearly two battalions of Ghurkas in addition to the special detachments and Indian troops nearer the Mesopotamian end of the line. Some detachments of Australian and Indian troops were observed and there were a number of Canadian and New Zealand officers on duty at headquarters in Hamadan. The officers accompanying the Dunster force, in addition to those belonging to the regular battalions of troops, were mostly picked men and considered to be especially capable.
I understand that the British now completely control the Caspian and its shipping and I know that bodies of marines, naval men, and inland water transportation men (the latter belonging to the Royal Engineers of the British army) are going at this time to the Caspian to take charge of the shipping. I have also been informed by military officers that these units probably number in all more than five hundred men and are taking with them guns of 4.7 size for mounting on ships in the Caspian, and parts for the building of mine sweepers. I was also told that some six inch naval guns were going up, but I do not believe that it would be possible to haul such heavy guns over the Bagdad-Caspian road in its present condition and with the present transportation facilities.