A modernized cog runs out of space before it runs out of weapon ideas

How would you modernize a medieval cog for twenty-first-century combat?

Add compact propulsion and power first, then modest guns and perhaps missiles, while recognizing that space and fire risk make the concept extremely constrained.

The hull's limited internal volume makes power generation and a compact diesel engine the starting requirements. A 20 mm weapon is plausible, and a 40 mm gun may be near the upper practical limit. Missiles add capability but also create a serious fire risk aboard a wooden vessel. Treating the cog as a stealth platform cannot remove the basic constraints imposed by space, fuel, and weapon integration.