replace:

<FreePromotions/>


with:


<FreePromotions>
	<FreePromotion>
		<PromotionType>PROMOTION_BLITZ</PromotionType>
		<bFreePromotion>1</bFreePromotion>
	</FreePromotion>
</FreePromotions>


The following is the whole ironclad unit section with the changes you suggested(I changed the combat strength to 18):

		<UnitInfo>
			<Class>UNITCLASS_IRONCLAD</Class>
			<Type>UNIT_IRONCLAD</Type>
			<UniqueNames/>
			<Special>NONE</Special>
			<Capture>NONE</Capture>
			<Combat>UNITCOMBAT_NAVAL</Combat>
			<Domain>DOMAIN_SEA</Domain>
			<DefaultUnitAI>UNITAI_RESERVE_SEA</DefaultUnitAI>
			<Invisible>NONE</Invisible>
			<SeeInvisible>NONE</SeeInvisible>
			<Description>TXT_KEY_UNIT_IRONCLAD</Description>
			<Civilopedia>TXT_KEY_UNIT_IRONCLAD_PEDIA</Civilopedia>
			<Strategy>TXT_KEY_UNIT_IRONCLAD_STRATEGY</Strategy>
			<Advisor>ADVISOR_MILITARY</Advisor>
			<bAnimal>0</bAnimal>
			<bFood>0</bFood>
			<bNoBadGoodies>0</bNoBadGoodies>
			<bOnlyDefensive>0</bOnlyDefensive>
			<bNoCapture>0</bNoCapture>
			<bRivalTerritory>0</bRivalTerritory>
			<bMilitaryHappiness>0</bMilitaryHappiness>
			<bMilitarySupport>1</bMilitarySupport>
			<bMilitaryProduction>1</bMilitaryProduction>
			<bPillage>1</bPillage>
			<bSabotage>0</bSabotage>
			<bDestroy>0</bDestroy>
			<bStealPlans>0</bStealPlans>
			<bInvestigate>0</bInvestigate>
			<bCounterSpy>0</bCounterSpy>
			<bFound>0</bFound>
			<bGoldenAge>0</bGoldenAge>
			<bInvisible>0</bInvisible>
			<bFirstStrikeImmune>0</bFirstStrikeImmune>
			<bNoDefensiveBonus>0</bNoDefensiveBonus>
			<bIgnoreBuildingDefense>1</bIgnoreBuildingDefense>
			<bCanMoveImpassable>0</bCanMoveImpassable>
			<bFlatMovementCost>0</bFlatMovementCost>
			<bIgnoreTerrainCost>0</bIgnoreTerrainCost>
			<bNukeImmune>0</bNukeImmune>
			<bPrereqBonuses>0</bPrereqBonuses>
			<bPrereqReligion>0</bPrereqReligion>
			<bMechanized>1</bMechanized>
			<bRenderBelowWater>1</bRenderBelowWater>
			<UnitClassUpgrades>
				<UnitClassUpgrade>
					<UnitClassUpgradeType>UNITCLASS_DESTROYER</UnitClassUpgradeType>
					<bUnitClassUpgrade>1</bUnitClassUpgrade>
				</UnitClassUpgrade>
			</UnitClassUpgrades>
			<UnitAIs>
				<UnitAI>
					<UnitAIType>UNITAI_ATTACK_SEA</UnitAIType>
					<bUnitAI>1</bUnitAI>
				</UnitAI>
				<UnitAI>
					<UnitAIType>UNITAI_RESERVE_SEA</UnitAIType>
					<bUnitAI>1</bUnitAI>
				</UnitAI>
			</UnitAIs>
			<NotUnitAIs/>
			<Builds/>
			<ReligionSpreads/>
			<GreatPeoples/>
			<Buildings/>
			<ForceBuildings/>
			<HolyCity>NONE</HolyCity>
			<ReligionType>NONE</ReligionType>
			<StateReligion>NONE</StateReligion>
			<PrereqReligion>NONE</PrereqReligion>
			<PrereqBuilding>NONE</PrereqBuilding>
			<PrereqTech>TECH_STEAM_POWER</PrereqTech>
			<TechTypes>
				<PrereqTech>NONE</PrereqTech>
				<PrereqTech>NONE</PrereqTech>
				<PrereqTech>NONE</PrereqTech>
			</TechTypes>
			<BonusType>BONUS_COAL</BonusType>
			<PrereqBonuses>
				<BonusType>NONE</BonusType>
				<BonusType>NONE</BonusType>
				<BonusType>NONE</BonusType>
				<BonusType>NONE</BonusType>
			</PrereqBonuses>
			<ProductionTraits/>
			<Flavors/>
			<iAIWeight>0</iAIWeight>
			<iCost>100</iCost>
			<iHurryCostModifier>0</iHurryCostModifier>
			<iMinAreaSize>20</iMinAreaSize>
			<iMoves>2</iMoves>
			<iAirRange>0</iAirRange>
			<iNukeRange>-1</iNukeRange>
			<iWorkRate>0</iWorkRate>
			<iBaseDiscover>0</iBaseDiscover>
			<iDiscoverMultiplier>0</iDiscoverMultiplier>
			<iBaseHurry>0</iBaseHurry>
			<iHurryMultiplier>0</iHurryMultiplier>
			<iBaseTrade>0</iBaseTrade>
			<iTradeMultiplier>0</iTradeMultiplier>
			<iGreatWorkCulture>0</iGreatWorkCulture>
			<TerrainImpassables>
				<TerrainImpassable>
					<TerrainType>TERRAIN_OCEAN</TerrainType>
					<bTerrainImpassable>1</bTerrainImpassable>
				</TerrainImpassable>
			</TerrainImpassables>
			<FeatureImpassables/>
			<iCombat>18</iCombat>
			<iAirCombat>0</iAirCombat>
			<iAirCombatLimit>0</iAirCombatLimit>
			<iXPValueAttack>4</iXPValueAttack>
			<iXPValueDefense>2</iXPValueDefense>
			<iFirstStrikes>0</iFirstStrikes>
			<iChanceFirstStrikes>0</iChanceFirstStrikes>
			<iInterceptionProbability>0</iInterceptionProbability>
			<iEvasionProbability>0</iEvasionProbability>
			<iWithdrawalProb>0</iWithdrawalProb>
			<iCollateralDamage>0</iCollateralDamage>
			<iCollateralDamageLimit>0</iCollateralDamageLimit>
			<iCollateralDamageMaxUnits>0</iCollateralDamageMaxUnits>
			<iCityAttack>0</iCityAttack>
			<iCityDefense>0</iCityDefense>
			<iAnimalCombat>0</iAnimalCombat>
			<iHillsDefense>0</iHillsDefense>
			<TerrainNatives/>
			<FeatureNatives/>
			<TerrainDefenses/>
			<FeatureDefenses/>
			<UnitClassAttackMods/>
			<UnitClassDefenseMods/>
			<UnitCombatMods/>
			<DomainMods/>
			<BonusProductionModifiers/>
			<iBombRate>0</iBombRate>
			<iBombardRate>10</iBombardRate>
			<SpecialCargo>NONE</SpecialCargo>
			<DomainCargo>NONE</DomainCargo>
			<iCargo>0</iCargo>
			<iConscription>0</iConscription>
			<iCultureGarrison>0</iCultureGarrison>
			<iExtraCost>0</iExtraCost>
			<iAsset>3</iAsset>
			<iPower>6</iPower>
			<UnitMeshGroups>
				<iGroupSize>1</iGroupSize>
				<fMaxSpeed>2.25</fMaxSpeed>
				<iMeleeWaveSize>1</iMeleeWaveSize>
				<iRangedWaveSize>1</iRangedWaveSize>
				<UnitMeshGroup>
					<iRequired>1</iRequired>
					<EarlyArtDefineTag>ART_DEF_UNIT_IRONCLAD</EarlyArtDefineTag>
				</UnitMeshGroup>
			</UnitMeshGroups>
			<Button>,Art/Interface/Buttons/Units/Ironclad.dds,Art/Interface/Buttons/Unit_Resource_Atlas.dds,8,9</Button>
			<HotKey/>
			<bAltDown>0</bAltDown>
			<bShiftDown>0</bShiftDown>
			<bCtrlDown>0</bCtrlDown>
			<iHotKeyPriority>0</iHotKeyPriority>
			<FreePromotions>
				<FreePromotion>
					<PromotionType>PROMOTION_BLITZ</PromotionType>
					<bFreePromotion>1</bFreePromotion>
				</FreePromotion>
			</FreePromotions>
		</UnitInfo>