The very first time I came across a box of hand grenades on the wreck was early in the project. The top of a heavily made, 5 sided wooden box had become exposed in the sediment. The sides of the box were about 50mm (2") thick and around the rim on the inside was lead sheeting. There was a fair amount of iron concretion on top but I could just make out round spherical shapes in the box. It required too much work and would have taken too long to attempt to raise the object at that time. Therefore, it was left alone until there was enough time to execute a careful excavation.
At the time, I thought the contents might be large iron shot but had to question the manner in which they were stored. Imagine my surprise when, after excavating the contents of the box some weeks later, they turned out to be Hand Grenades.
Rather than a lengthy and difficult explanation, the images below, drawn by diver John Terry, show how they were made.
A total of thirty complete hand grenades were recovered from the bow section of the Invincible and most were stored in antiquity in very heavily made wooden boxes. The first box had five sides, which we assume was made that way to fit in a compartment. The rest however, were four sided measuring 600mm x 600mm x 242mm ht. Each grenade had a hollow wooden fuse made from beech and every grenade was fully primed with black gunpowder and ready for action.

The conservation was undertaken in three stages, one for each different material. First there was the canvas cover, then the wooden fuses and finally came the difficult bit - the cast iron. Conserving metal objects is always time consuming and difficult and these were no exception. The Portsmouth City Museum conservator, Simon Aked, employed a process using a "hydrogen reduction furnace". This process is very expensive and time consuming and so in order to maximise efficiency of the furnace, we waited until it was being used on other items from various museums ensuring enough space to add our little grenades. The results were brilliant.

To understand how hydrogen reduction works folllow this link - hydrogen reduction.

After they had been conserved and were completely stable, Arthur and I took one of them to the Army museum in London where the curator allowed us to compare them to the army ones of the same period. Another surprise awaited us when we found the Army ones to be much smaller and lighter than those found on Invincible. Of course, on board all British Men-O-War there were marines who were masters at close combat. Our research showed that our grenades were thrown by the Marines from way up on the "fighting tops" down onto enemy decks.