252 ON THE DEFENCES OF PORT JACKSON, 



The best position for booms is necessarily where obstructions 

 already exist. The " Sow and Pigs" Shoal leaving two narrow 

 channels, one on each side, presents greater facilities for placing 

 obstructions than any other position. 



If booms are only floated or laid the whole distance from 

 the Sow and Pigs Rock to the shores, large vessels at full speed 

 would most likely pass over them by forcing them down; they 

 could undoubtedly accomplish this by sending boats over night to 

 prepare a gap in the booms by attaching bags of shot or other 

 weights to them to diminish their buoyancy, or by blowing them 

 partly away with torpedoes. Such booms could not prevent boats 

 passing across or over them at night for the purpose of landing 

 large bodies of troops within the obstructions for a coup de main 

 on our batteries. 



If to remove these objections we make our obstructions in 

 the form of dykes, leaving only a small opening in each channel 

 for navigation, the scheme becomes more feasible, as it must be 

 self-evident that it is easier to boom and to command a narrow 

 channel of from 300 to 400 yards than 1700 or 1800 yards, the 

 whole distance from shore to shore. Engineers differ in 

 opinion with regard to the probable results that dykes con- 

 structed across the Sow and Pigs Shoal might produce in Port 

 Jackson, and it certainly is a most interesting subject for discus- 

 sion. Booming small openings is merely a matter of engineering 

 detail ; a plan could be devised for obstructing these channels 

 temporarily in time of war. 



Booms would require powerful batteries to protect them, and 

 the best positions for these batteries would be at point blank 

 ranges from the obstructions. 



George Head and Green Point are preferable to Middle Head 

 and Inner South Head for Head-quarters and batteries, for if booms 

 are to detain an enemy, it is better to engage vessels at short 

 ranges in narrow passages where turning and manoeuvring is 

 impossible, and where every one of our shots would tell from our 

 knowing by previous target practice the exact range arid elevation 

 for every point in the channels, than to engage them partly at 

 sea where the costly ammunition of our heavy guns would be 

 mostly wasted. It is hardly probable that an enemy would 



