Looking from a Bomb-Proof

The back reads: "This picture, taken from one of the bomb-proofs in the rear of the fighting line of the Japanese, gives a very good idea of the heights of Port Arthur on which the frowning forts were erected...."
The text ends with an enigmatic "A8833". Hmmm.
And what are "frowning forts"?

This stereoscope was found at a flea market in Columbia, Missouri amidst antique cracked tea cups, photographs of other people's ancestors, and bird feathers. Strange and amazing in its simultaneous banality and poignancy, the photograph on the front shows a blurry and oddly framed landscape partly obscured on the top by what appears to be a clumsy photographer's equipment. Actually, the photograph was taken below ground level from inside a bomb-proof shelter. The The back recounts a story of war on the frontlines of the Battle of Port Arthur - the hazy mountains in the background. An oddly calm and bucolic image for the bloody skirmishes. The awkward composition - seemingly made in an attempt to place the viewer "in the thick of battle" inside the bomb-proof - has the effect of inspiring strange narratives: What spy is looking out on the range? Are we seeing the world from the eyes of aliens crawling out from their space ship? Who else would photograph this seemingly unexceptional scene? Is this a glimpse at the apocalyptic future? And for whom was this stereoscope made for and what did they glean from it?

About the Battle of Port Arthur:
The Battle of Port Arthur (February 8-9, 1904) is considered the starting battle of the Russo-Japanese War. It began with a surprise night attack by a squadron of Japanese destroyers on the Russian fleet anchored at Port Arthur, Manchuria, and continued with further skirmishing until May 1904. Losing at Port Arthur for the Russians — and especially for Tsar Nicholas II — was fraught with dire circumstances for the Imperial Russian regime as the Russian people lost confidence in the military and government. The Russo-Japanese War is believed to have been a direct causal factor for the Russian Revolution of 1905.