# UNDF: UNDF-2026-000000975
--- a/src/projectiledef.h
+++ b/src/projectiledef.h
@@ -22,7 +22,7 @@
 #ifndef __INCLUDED_PROJECTILEDEF_H__
 #define __INCLUDED_PROJECTILEDEF_H__

-#include "basedef.h"
+#include "basedef.h"  // SIMPLE_OBJECT, BASE_OBJECT, OBJ_PROJECTILE
 #include "lib/gamelib/gtime.h"

-#include <vector>
+#include <unordered_set>


 enum PROJ_STATE
@@ -49,7 +49,7 @@
 	WEAPON_STATS   *psWStats;               ///< firing weapon stats
 	BASE_OBJECT    *psSource;               ///< what fired the projectile
 	BASE_OBJECT    *psDest;                 ///< target of this projectile
-	std::vector<BASE_OBJECT *> psDamaged;   ///< the targets that have already been dealt damage to (don't damage the same target twice)
+	std::unordered_set<BASE_OBJECT *> psDamaged; ///< the targets that have already been dealt damage to (O(1) lookup instead of O(N) linear scan)

 	Vector3i        src = Vector3i(0, 0, 0); ///< Where projectile started
 	Vector3i        dst = Vector3i(0, 0, 0); ///< The target coordinates
--- a/src/projectile.cpp
+++ b/src/projectile.cpp
@@ -376,7 +376,7 @@
 		psProj->rot.direction, psProj->rot.pitch, psProj->rot.roll,
 		psProj->state,
 		(int)psProj->expectedDamageCaused,
-		(int)psProj->psDamaged.size(),
+		(int)psProj->psDamaged.size(),  // unchanged: .size() works on unordered_set
 	};
 	_syncDebugIntList(function, "%c projectile = p%d;pos(%d,%d,%d),rot(%d,%d,%d),state%d,expectedDamageCaused%d,numberDamaged%u", list, ARRAY_SIZE(list));
 }
@@ -869,7 +869,7 @@
 		BASE_OBJECT *psTempObj = *gi;
 		CHECK_OBJECT(psTempObj);

-		if (std::find(psProj->psDamaged.begin(), psProj->psDamaged.end(), psTempObj) != psProj->psDamaged.end())
+		if (psProj->psDamaged.count(psTempObj) != 0)
 		{
 			// Dont damage one target twice
 			continue;
@@ -950,7 +950,7 @@
 			asWeap.nStat = psStats - asWeaponStats.data();

 			// Assume we damaged the chosen target
-			psProj->psDamaged.push_back(closestCollisionObject);
+			psProj->psDamaged.insert(closestCollisionObject);

 			spawnedProjectile = proj_SendProjectileInternal(&asWeap, psProj, psProj->player, psProj->dst, nullptr, true, -1);
 		}
@@ -1290,7 +1290,7 @@

 			if (relativeDamage >= 0)	// So long as the target wasn't killed
 			{
-				psObj->psDamaged.push_back(psObj->psDest);
+				psObj->psDamaged.insert(psObj->psDest);
 			}
 		}
 	}
@@ -1396,7 +1396,10 @@
 		setProjectileDestination(psObj, nullptr);
 	}
 	// Remove dead objects from psDamaged.
-	psDamaged.erase(std::remove_if(psDamaged.begin(), psDamaged.end(), [](const BASE_OBJECT *psObj) { return ::isDead(psObj); }), psDamaged.end());
+	for (auto it = psDamaged.begin(); it != psDamaged.end(); )
+	{
+		it = ::isDead(*it) ? psDamaged.erase(it) : std::next(it);
+	}

 	// This extra check fixes a crash in cam2, mission1
 	if (worldOnMap(psObj->pos.x, psObj->pos.y) == false)
@@ -1954,9 +1957,9 @@
 		checkObject(psProjectile->psSource, location_description, function, recurse - 1);
 	}

-	for (unsigned n = 0; n != psProjectile->psDamaged.size(); ++n)
+	for (const auto *psObj : psProjectile->psDamaged)
 	{
-		checkObject(psProjectile->psDamaged[n], location_description, function, recurse - 1);
+		checkObject(psObj, location_description, function, recurse - 1);
 	}
 }