Index: binaries/data/mods/public/gui/session/selection_details.js
===================================================================
--- binaries/data/mods/public/gui/session/selection_details.js
+++ binaries/data/mods/public/gui/session/selection_details.js
@@ -80,9 +80,13 @@
 	// Rank
 	if (entState.identity && entState.identity.rank && entState.identity.classes)
 	{
+
+		let rankObj = GetTechnologyData("unit_" + entState.identity.rank.toLowerCase(), playerState.civ);
+		let rankDescription = (rankObj ? "\n" + rankObj.tooltip : "");
+
 		Engine.GetGUIObjectByName("rankIcon").tooltip = sprintf(translate("%(rank)s Rank"), {
 			"rank": translateWithContext("Rank", entState.identity.rank)
-		});
+		}) + rankDescription;
 		Engine.GetGUIObjectByName("rankIcon").sprite = "stretched:session/icons/ranks/" + entState.identity.rank + ".png";
 		Engine.GetGUIObjectByName("rankIcon").hidden = false;
 	}