Just added this a Australian Navy Sestrel Deck clock.

[stefaulkner]

The anchor may tie it back to Birmingham as referred to Reeny earlier. The anchor is the symbol used by the Birmingham Assay Office.

[Reeny]

According to Wiki - the ship entered service 1925, but the ships role was re-assigned during 1942.
So rather than being a calibration mark or serial number - it is more likely that the Anchor stamp is an AU Navy or manufacturers issue mark for new equipment installed during an upgrade in 1942, or there was change of Captain (and the Captain wanted a new clock)

In February 1942, the Australian cruiser became flagship of the newly formed ANZAC Squadron.^[21]
In early March, Australia was assigned to shell Gasmata in New Britain.^[38]
However, on 7 March, the ships for the operation were recalled, and were used three days later to provide long-range protection for the American aircraft carriers USS Lexington and USS Yorktown

Edit - I have just noticed British Made printed on the dial.
So Stefaulkers suggestion that this is the Birmingham Factory mark makes sense.

[River Rat]

Have emailed the Australian navy museum and Australian war museum with photos only got a reply from the Australian war museum they received my question still waiting for what they think of it. One member of MWR forum said maybe it will return to Australia one day made me think. I am getting old so later when I start thinning out the collection due to, I am getting up in years so some time down the road might donate it to one of those museums a ship named after your country was a nations pride and I bet they don't have a lot of historical items from this ship. Plus, my dad's mom was from Australia.

[River Rat]

Some photos of the movement. Has an Elliott movement. Clean movement looks to have been serviced a plus. Has a cover over the regulator never seen that yet on an Elliott clock movement before.