Your "naval experience apparently makes you an "expert" on the type of weaponry available in 1916 - sure it does!!

Tell me Jom do you know why in the British Isles we have Ordnance Survey Maps? Can you tell us all about how they came into being in 1791?

To obtain what is known as the "Firing Solution" for any piece of artillery you have to know the position of the target, the elevation of the target and the gun platform respectively and the horizontal distance between gun and target. You then have to find a thing called "the error of the day" which takes into account humidity, temperature, wind speed and direction and barometric pressure all of which were perfectly capable of being measured then as they can be now. Now back in 1916:

Any OS map of Dublin City would give the position of any target
The tide tables for Dublin would give the height of the gun platform (In this case a moored ship) while the OS Map would give height above sea level as well as the horizontal range between the Helga and whatever building was being targeted. The ballistic characteristics of the gun are a known quantity and the competence of the gunnery team known (Their training after all would be to hit a moving target from their own moving ship - In the case we are talking about both target and ship are stationary making it even simpler) - as previously stated a simple matter of applied mathematics - no-one would have to be an expect to state the above, all it takes is common sense. As someone else pointed out the Patrol Ship Helga fired 40 shots over the period of the Rising - Again from personal experience a hand served 4.5" QF Gun with an experienced crew is capable of firing 24 rounds per minute, the Helga was fitted with a 3" QF Gun firing fixed ammunition so her rate of fire would have been even quicker. As far as knowledge of gunnery goes - yours would appear to be non-existent.

By 1917 the performance of each gun firing over a prolonged period was known so that as the barrels heated and the rifling wore down the elevation could be adjusted to ensure that the shells fired did not fall short.

By the way the Henry I was referring to was Henry II NOT Henry VIII. He gave permission for an expedition to be sent to Ireland to curb raids from Ireland on the British mainland. By force of arms which was the way disputes were settled in those times the Kings of Ireland swore an oath of fealty to Henry II. Note Kings plural so Ireland was not a united country in an attempt to establish a uniform peace a High King was elected this however was by no means successful.