Two summer cruises with the Baltic fleet in 1854-5: being the log of the 'Pet' ... By Robert Edgar Hughes

This book is online. Basically it is a first hand account of the Bomarsund campaign written from the perspective of a civilian observer - this case being a yachting reverend. Just to give you a taste here's his account of a British camp
The camp was singularly pretty and picturesque. The sappers had built themselves the neatest little huts of small fir branches with the stump upwards, so that they formed a snug roof almost as waterproof as thatch, and very pretty to look at. Jack, more ambitious, had hewn off large branches with his cutlass, and placed them as they grow. This arrangement produced fine roomy huts, but a large supply of accidental doors and unintentional windows made a pleasing variety, and afforded the inmates an opportunity of contemplating the motions of the heavenly bodies. The officers of the " Acre" had a splendid bell tent, as big as a bullock-shed; but the most striking thing in the tent way was the Colonel's;—this consisted of a single blanket stretched over a pole and strained tightly down to the ground; into this the gallant officer crawled all fours whenever sleep assailed his weary eyes. A number of military accoutrements, and, if I remember right, a little strip of a flag, gave splendour and dignity to the domicile; and I think on the whole the Colonel used to turn out in the morning about the smartest and best shaved man in the camp. I must confess that the French camp gave the impression that they were professional performers, and ours that we were amateurs ; and yet here were our fellows with their handful of men in the advanced position, well within gunshot, and perfectly in the humour to receive anything in the way of shot and shell, bayonet or cutlass, that the enemy might feel inclined to offer. After a time, we amateurs began to stroll about and endeavour to understand the topography of the place; the sentries, however, had orders to allow no one to pass to the front, and our walk was rather circumscribed. Presently, however, a sentry seeing that one of us had a glass, beckoned to us to approach, and swore that he had seen half a dozen fellows in long dark cloaks crouching among the bushes before him. We watched for some time, but the sentry's eyes were sharper than ours, and we could make nothing of it.