BY G. A. MOEELL, ESQ., C.E. 251 



shipping. The strongest work of such a system should be at 

 Bradley Head as a centre of operation, the batteries at the 

 Heads being subsidiary ; the heaviest of guns would be required 

 at every work, with a large number of men and good military 

 roads to every position. 



This system is the most rational, and the only one in accord- 

 ance with the laws of Defence and Attack, but it is too costly to 

 be entertained at present by the Colony. I find from a rough 

 estimate that it would not cost less than a quarter of a million 

 sterling before its completion, and not less than 60,000 annually 

 for the maintenance of the necessary troops and for repairs. 



The second system of defence consists in obstructing the 

 Channels at the entrance of the Harbour, and in concentrating 

 round these obstructions, where vessels may be expected to be 

 delayed, our strongest works, making provision, however, 

 for the possibility of vessels taking us by surprise or for 

 their forcing a passage, by constructing subsidiary works within 

 the obstructions. 



Movable obstructions beyond booming a narrow channel or 

 canal are not generally considered as means of defence, but we 

 are obliged to take into consideration the small number of 

 troops at our command and the cost of Defensive Works. 

 If mechanical contrivances could be relied on, a small open- 

 ing might be left in the obstructions of the channels to be closed 

 at a short notice on the appearance of suspicious craft. 

 Any obstructions must be made of as permanent a character 

 as possible to prevent boats intended to land troops from passing 

 over them or blowing them up partly, to effect a coup de main on 

 our batteries. 



The cost of the construction of this second system of defence 

 would not be half that of the first, and the expense for main- 

 tenance would be within our means ; but its efficiency would also 

 be proportionately diminished, as so much depends upon obstruc- 

 tions which a powerful and ingenious enemy might succeed in 

 clearing away. 



I have carefully considered this second system consisting of 

 obstructions and batteries to protect them, and I shall now refer 

 to it more particularly. 



