The scenario was based on the Battle of Salamis (Crete), 306 BCE fought between an Antigonid fleet led by Demetrius and a Ptolemaic fleet led by Ptolemy in person. The main source for the battle is Diodorus.
The units in the game (4 models on a base) represent about 10 ships each. Miniatures are primarily Langton 1:1200 and Navwar 1:1200, with a few Valiant 1:900 and scratch-built ships.
As described in Diodorus, the Antigonid fleet deploys first, and the Ptolemaic fleet second.
The 1/1200 scale ancient ships were temporarily re-based for Hail, Agrippa! simply by sticking the old individual bases to cardboard. In order to use the same ships for various game systems, they are being fitted with rare earth magnets. Custom 40 mm x 130 mm magnetic hardboard bases were made by Good Ground LLC. The magnetic material on the bases is intended for transport using steel drawers. Here they are being used upside down so the rare earth magnets on the ships will stick. This allows for variations in the type, number and positions of ships.
[Edit: Since the Good Ground bases are magnetic, a piece of ferrous metal on the bottom of the ship model works as well or better than a rare earth magnet. My recent ships have been built using a small zinc-plated steel washer or a square of tin-plated steel sheet. This is easier and cheaper than the magnets.]
The scenario was loosely based on the Battle of Cos, 258 BCE (or 261, or whenever; nobody knows) fought between an Antigonid fleet and a Ptolemaic fleet. The order of battle was determined by the miniatures available, and included ships as large as deceres (or dekeres) which are probably heavier than any at the real battle. Fleets of this period might be 100-200 ships, so the units (4 models on a base) might represent 9-18 ships.
Miniatures are primarily Langton 1:1200 and Navwar 1:1200, with a few Valiant 1:900 and scratch-built ships.